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5α-dihydrotestosterone (DHT)
An androgen that plays an important role in the development of the male external genitalia.
The enzyme that converts testosterone to 5α-dihydrotestosterone.
5α-reductase deficiency
The congenital absence of the enzyme 5α-reductase, which converts testosterone to dihydrotestosterone.


A skin disorder caused by blockage and inflammation of sebaceous glands.
acquired immune deficiency syndrome (AIDS)
The disease caused by the human immunodeficiency virus (HIV); its onset is defined by the occurrence of any of a number of opportunistic infections, or on the basis of blood tests.
A structure at the front of a sperm that contains enzymes and receptors required for penetration of the zona pellucida of an ovum.
acrosome reaction
The opening of a sperm’s acrosome, releasing enzymes necessary for penetration of the zona pellucida of the ovum.
A fetishistic interest in amputees or amputation stumps.
action potential
An electrochemical signal that travels rapidly along an axon.
activational effect
The influence of a sex hormone on the function of brain circuitry in adulthood.
A drug used in the treatment of genital herpes.
Helping the propagation of an organism’s genes.
A method of tubal sterilization that blocks the oviduct with small plugs.
The period of psychosexual and social maturation that accompanies and follows puberty.
adrenal gland
A gland near the kidney that secretes a variety of steroids, including sex steroids.
adult baby
An adult who obtains sexual satisfaction from acting as a baby or toddler.
adult bookstore
Euphemism for a store dealing in pornography.
Carrying signals toward the CNS.
The placenta, whose delivery constitutes the final stage of labor.
Sexual behavior engaged in after coitus or orgasm, or at the end of a sexual encounter.
AIDS dementia
A broad cognitive impairment caused by HIV infection.
A protein whose presence at elevated levels in the blood of a pregnant woman is suggestive of neural tube defects in the fetus.
alveolus (pl. alveoli)
Microscopic cavity, such as one of those in the breast where milk is produced.
Absence of menstruation.
The sampling of the amniotic fluid for purposes of prenatal diagnosis.
The membranous sac containing amniotic fluid and the fetus.
amniotic fluid
The fluid within which the fetus develops.
The middle portion of the oviduct, where fertilization usually occurs.
Tending to increase tissue mass.
anal fold
The posterior portion of the urethral fold, which gives rise to the anus.
anal sex
Penetration of the anus by the penis, or any sexual behavior involving the anus.
Researcher who studies the structure of the body.
Any of a class of steroids—the most important being testosterone—that promote male sexual development and that have a variety of other functions in both sexes.
androgen insensitivity syndrome (AIS)
An intersexed condition caused by absent or nonfunctional androgen receptors.
In men, the gradual decline of fertility with age; a hypothetical male equivalent of menopause.
Sexually attracted to men.
Sexual contact between the mouth or tongue and the partner’s anus.
Difficulty experiencing or inability to experience orgasm. In women, also called female orgasmic disorder.
The study of cultural or biological variations across the human race.
anti-Müllerian hormone (AMH)
A peptide hormone secreted by Sertoli cells of the testis that prevents the development of the female internal reproductive tract.
antiretroviral drugs
Drugs effective against retroviruses.
A cavity that forms in an ovarian follicle as it matures.
The exit of the gastrointestinal tract.
A substance believed to improve sexual performance, enhance sexual pleasure, or stimulate desire or love.
A fetishistic interest in having an amputation.
The circular patch of darker skin that surrounds the nipple.
The enzyme that converts testosterone to estradiol.
artificial insemination
An assisted reproduction technique that involves the placement of semen in the vagina or uterus with the aid of a syringe or small tube.
artificial insemination by donor (AID)
Artificial insemination using sperm from a man who is not the woman’s partner.
Describes a person who never experiences sexual attraction.
asexual reproduction
Reproduction in which all the offspring’s genes are inherited from a single parent.
assisted reproductive technology (ART)
In vitro fertilization and related technologies.
asymptomatic carrier
Someone who is infected with a disease organism but is not experiencing symptoms.
attachment theory
The idea that relationship styles are influenced by the quality of the early parent–child bond.
Providing sexual stimulation to oneself or being aroused sexually by oneself.
autoerotic asphyxia
Self-strangulation for purposes of sexual arousal.
A form of male-to-female transexuality characterized by a man’s sexual arousal at the thought of being or becoming a woman.
autonomic ganglion
A cluster of autonomic neurons outside the CNS.
autonomic nervous system
The portion of the nervous system that controls smooth muscles and glands without our conscious involvement.
Any chromosome other than a sex chromosome.
aversion therapy
A form of behavior therapy that attempts to eliminate unwanted desires or behaviors by associating them with some unpleasant experience, such as a noxious smell.
axon (or nerve fiber)
The extension of a neuron that conveys impulses, usually in a direction away from the cell body. Also called nerve fiber.


bacterial vaginosis
A condition in which the normal microorganisms of the vagina are replaced by other species, causing discomfort and a foul-smelling discharge.
Inflammation of the glans of the penis.
bar mitzvah
Jewish coming-of-age ceremony for boys.
barrier method
Any contraceptive technique in which a physical barrier, such as condom or diaphragm, prevents sperm from reaching the ovum.
Bartholin’s glands
Glands at the introitus that discharge a small amount of fluid during sexual arousal.
basal body temperature (BBT)
Body temperature measured in the morning before getting out of bed.
basal ganglia
Deep noncortical structures of the forebrain.
bat mitzvah
Jewish coming-of-age ceremony for girls.
A facility, usually in the form of a private club, used for casual sex between men.
battered-woman syndrome
A version of post-traumatic stress disorder affecting women who are victims of intimate partner violence, characterized especially by a cessation of attempts to escape from the abusive situation.
An all-inclusive term for forms of sexual expression that involve inflicting and receiving physical pain, restraint, or humiliation. Often construed as a compressed acronym for bondage and discipline, dominance and submission, and sadism and masochism.
In gay slang, a burly gay man with plenty of body hair; more generally, a member of a gay male subculture that rejects many of the prevailing standards of gay male attractiveness and behavior.
behavior therapy
Treatment of paraphilias or other disorders based on conditioning or other theories of behavioral psychology. Also called behavior modification.
behavioral couples therapy (BCT)
Therapy focused on improving styles of communication between partners in relationships.
benign prostatic hyperplasia
Noncancerous enlargement of the prostate gland.
Obsolete term for sexual contact between a person and an animal.
Colloquial term for bisexual.
In law, the crime of marrying someone while already married to another spouse.
A tissue sample from a living person for diagnostic or (less commonly) for therapeutic purposes.
Prejudice against bisexuals.
birth canal
The canal formed by the uterus, cervix, and vagina, through which the fetus passes during birth.
birthing center
A facility specializing in childbirth care.
Sexual attraction to persons of both sexes.
A conceptus shortly before implantation, when it takes the form of a sphere of cells with a central cavity.
The use of physical restraint for purposes of sexual arousal.
Boston marriage
In 19th-century New England, the cohabitation of two women.
An aromatic aldehyde that attracts spermatozoa to the ovum.
Bradley method
A method of childbirth instruction that stresses the partner’s role as birth coach and that seeks to avoid medical interventions.
The region of the brain between the forebrain and the spinal cord.
Braxton-Hicks contractions
Irregular uterine contractions that occur during the third trimester of pregnancy. Also called false labor.
breast bud
The first stage of breast development at puberty.
breast ironing
A West-African custom of pounding a girl’s breasts with the intent of delaying their development.
A house of prostitution.
bulbospongiosus muscle
A muscle that attaches to the base of the clitoris or penis and assists with erection and (in men) ejaculation. In women, the internal portion of the muscle surrounds the introitus.
bulbourethral glands
Two small glands near the root of the penis whose secretions (“pre-cum”) may appear at the urethral opening during sexual arousal prior to ejaculation. Also known as Cowper’s glands.
Masculine-acting, often used to describe certain lesbians.


calendar rhythm method
A fertility awareness method of contraception that takes account of variability in the length of a woman’s menstrual cycles.
call girl
An escort-service prostitute, especially one who is relatively upscale in terms of clientele and price.
A fungal infection of the vagina. Also called thrush or a yeast infection.
A chemical change in the surface of a sperm within the female reproductive tract that allows it to swim more forcefully and respond to the presence of the ovum.
An array of protein molecules surrounding the core of a virus.
casual sex
Sexual encounters that do not take place within a durable sexual relationship.
CD4 lymphocytes
A type of lymphocyte that carries the CD4 receptor; one of the major targets of HIV.
CD4 receptor
A receptor in the cell membrane of CD4 lymphocytes.
Living under a vow not to marry or (by implication) to engage in sexual relations.
cell body
The part of a neuron where the nucleus is located.
central nervous system (CNS)
The brain and spinal cord.
cerebral cortex
Convoluted, layered gray matter that covers most of the brain.
cerebral hemispheres
The uppermost and largest portion of the brain, divided into left and right halves.
cervical cap
A small rubber or plastic cap that adheres by suction to the cervix, used as a contraceptive.
cervical mucus
Mucus, the consistency of which varies around the menstrual cycle, secreted by glands in the cervix.
cervical mucus method
A fertility awareness method of contraception that depends on observing changes in the cervical mucus.
The lowermost, narrow portion of the uterus that connects with the vagina.
cesarean section (C-section)
The delivery of a baby through an incision in the abdominal wall and the uterus.
A primary sore on the skin or a mucous membrane in a person infected with syphilis. (Pronounced SHANK-er.)
child molester
An adult who has had sexual contact with a prepubescent child.
A sexually transmitted disease caused by infection with the bacterium Chlamydia trachomatis.
chorionic villus sampling
The sampling of tissue from the placenta for purposes of prenatal diagnosis.
A rod-shaped nuclear organelle composed of DNA and associated proteins.
chronic pelvic pain syndrome
An alternative, more-inclusive term for chronic prostatitis.
Microscopic, hairlike extensions of cells, often capable of a coordinated beating motion.
civil commitment
Detention of a person with a mental disorder that creates a threat to himself or others.
classical (Pavlovian) conditioning
A form of behavioral learning in which a novel stimulus is tied to a preexisting reflex.
The transition to infertility at the end of a woman’s reproductive life, lasting for several years and culminating in menopause.
clinical psychology
The assessment or treatment of mental or behavioral problems, as practiced by a psychologist.
clitoral hood
A loose fold of skin that covers the clitoris.
Removal of the entire external portion of the clitoris (glans, shaft, and hood).
The erectile organ in females, whose external portion is located at the junction of the labia minora, just in front of the vestibule.
The common exit of the gastrointestinal and urogenital systems; in humans it is present only in embryonic life.
A receptor that plays a secondary role in binding.
Related to the aspects of the mind that process knowledge or information.
cognitive psychology
The study of the information-processing systems of the mind.
cognitive therapy
Therapy based on changing a person’s beliefs and thought processes.
A live-in sexual relationship between two persons who are not married to each other.
coital alignment technique (CAT)
A variation of the man-above position for coitus that increases clitoral stimulation.
Penetration of the vagina by the penis.
The milk produced during the first few days after birth; it is relatively low in fat but rich in immunoglobulins.
The examination of the cervix with the aid of an operating microscope.
come out of the closet
(or “come out”) Reveal a previously concealed identity, such as being gay.
The cognitive component of love: the decision to maintain a relationship.
companionate marriage
A form of marriage in which the husband and wife are expected to be emotionally intimate and to engage in social activities together.
compulsive sexual behavior
Sexual behavior perceived subjectively as involuntary and diagnosed as a symptom of a compulsive disorder. Also called obsessive–compulsive sexual disorder.
Fertilization of the ovum.
The developing organism from the 2-cell stage onward, including both embryonic and extraembryonic tissues.
A woman who cohabits with a man but is not his wife, usually in polygamous cultures.
The modification of behavior by learning through association and/or reinforcement.
congenital adrenal hyperplasia (CAH)
A congenital defect of hormonal metabolism in the adrenal gland, causing the gland to secrete excessive levels of androgens.
Contact between two bacteria accompanied by the transfer of a short stretch of DNA from one to the other.
constant-dose combination pill
An oral contraceptive regimen in which all pills (except any dummy pills) contain the same drug dosage.
contraceptive implant
A device implanted in the body that slowly releases a hormonal contraceptive.
In childbirth, a periodic coordinated tightening of the uterine musculature, felt as a cramp.
control group
A group of subjects included in a study for comparison purposes.
Coolidge effect
The revival of sexual arousal caused by the presence of a novel partner.
Sexual intercourse, or coitus.
The rim of the glans of the penis.
corpus callosum
A band of axons interconnecting the left and right cerebral hemispheres.
corpus cavernosum (pl. corpora cavernosa)
Either of two elongated erectile structures within the penis or clitoris that also extend backward into the pelvic floor.
corpus luteum
A secretory structure in the ovary derived from an ovarian follicle after ovulation.
corpus spongiosum
A single midline erectile structure. In both sexes it fills the glans; in males it extends backward along the underside of the penis, surrounding the urethra.
The outer portion of an anatomical structure, as of the cerebral hemispheres or the adrenal gland.
courtship behavior
Behavior that attracts a mate.
courtship disorder
A paraphilia or cluster of paraphilias seen as a disorder of normal courtship behavior.
Pregnancy-like symptoms in the male partner of a pregnant women.
covenant marriage
A form of marriage that requires a stronger vow of commitment than a regular marriage and that makes divorce harder to obtain.
covert sensitization
A variation of aversion therapy in which the unpleasant experience is provided by the subject’s own imagination.
cremaster muscle
A striated muscle that wraps around the spermatic cord and the testis.
Wearing the clothing of the other sex, for any of a variety of reasons.
The appearance of the fetal scalp at the vaginal opening.
crus (pl. crura)
Internal extension of a corpus cavernosum of the clitoris or penis.
Failure of one or both testicles to descend into the scrotum by 3 months of postnatal age.
cultural psychology
The study of the interactions between culture and mental processes or behaviors.
cumulus cells
A layer of cells, derived from the granulosa cells of an ovarian follicle, that surrounds the ovum after ovulation.
Sexual contact between the tongue or mouth of one person and the vulva of another.
Stalking via the Internet.
cycle of abuse
The cycle in which some abused children 
grow up to repeat similar forms of abuse on others. Also called victim–perpetrator cycle.


A sheet of smooth muscle underlying the skin of the scrotum, which when contracted causes the skin to become thick and wrinkled.
date rape
Rape between dating or socially acquainted couples. Also called acquaintance rape.
dating relationship
A nonmarital sexual relationship between two persons who do not live together but who see each other on a more-or-less regular basis.
Removal of laws that criminalize activities such as prostitution.
deep kissing
Kissing, with entry of the tongue into the partner’s mouth.
delayed ejaculation
Difficulty achieving or inability to achieve orgasm or ejaculation. Also called male orgasmic disorder.
delayed labor
Labor that occurs more than 3 weeks after a woman’s due date.
delayed puberty
Failure of onset of puberty by some criterion age, usually 13 or 14 in girls and 14 in boys.
delusional jealousy
Persistent false belief that one’s partner is involved with another person.
delusional stalking
Stalking motivated by the delusional belief that the victim is in love with, or could be persuaded to fall in love with, the stalker.
The extensions of a neuron that receive incoming signals from other neurons.
An injectable form of medroxyprogesterone acetate, used as a contraceptive in women or to decrease the sex drive in male sex offenders.
Depo-SubQ Provera
A form of Depo-Provera designed for subcutaneous injection.
depressive psychosis
Depression accompanied by seriously disordered thinking.
designer steroids
Synthetic steroids intended to evade detection in drug tests.
An Indian temple prostitute.
A barrier placed over the cervix as a contraceptive.
diethylstilbestrol (DES)
A synthetic estrogen receptor agonist that was once used to prevent miscarriage but that caused cancer and fertility problems in some of the daughters born of these pregnancies.
In childbirth, the expansion of the cervical canal. Also called dilatation.
dilation and evacuation (D&E)
A procedure involving the opening of the cervix and the scraping out of the contents of the uterus with a curette (spoonlike instrument). D&E may be done as an abortion procedure or for other purposes.
A sex toy, often shaped like a penis, used to penetrate the vagina or anus.
Possessing the full complement of chromosomes.
discrepant sexual desire
The situation in which one partner in a relationship has much more interest in sex than the other.
disorders of sex development
An alternative term for intersexed conditions.
The distancing of oneself from the emotions evoked by some traumatic experience or memory.
DNA (deoxyribonucleic acid)
The linear molecule that forms the chemical basis of genes in all species except some viruses.
The use of humiliation or subservience for purposes of sexual arousal.
A woman who acts the role of the dominating partner in a BDSM setting.
A catecholamine that serves as a neurotransmitter and also as a hormone, inhibiting the release of prolactin from the anterior lobe of the pituitary gland.
dorsal horn
The rear portion of the gray matter of the spinal cord; it has a sensory function.
dorsal root
A bundle of sensory axons that enters a dorsal horn of the spinal cord.
To rinse the vagina out with a fluid; the fluid so used.
Down syndrome
A collection of birth defects caused by the presence of an extra copy of chromosome 21.
The wearing of exaggeratedly feminine clothing by a man, often for entertainment purposes.
Menstruation accompanied by pain.
Pain during coitus.


The upper, outermost layer of embryonic cells, which give rise to the skin and most of the nervous system.
ectopic pregnancy
Implantation and resulting pregnancy at any site other than the uterus.
Thinning of the cervix in preparation for childbirth.
Carrying signals away from the CNS.
ejaculatory duct
Either of the two bilateral ducts formed by the junction of the vas deferens and the duct of the seminal vesicle. The ejaculatory ducts empty into the urethra within the prostate.
elective abortion
An abortion performed in circumstances when the woman’s health is not at risk.
A form of emergency contraception that is effective for 5 days after sex.
The portion of the conceptus that develops into the fetus. The term is used loosely to describe the entire conceptus from the 2-cell stage onward.
embryonic stem cell
A cell found in the inner cell mass of the blastocyst, capable of developing into any type of cell.
emergency contraception
Use of high-dose contraceptives to prevent pregnancy after unprotected sex.
The loading of the constituents of semen into the posterior urethra immediately before ejaculation.
emotional jealousy
Fear that one’s partner is becoming emotionally committed to another person.
emotionally focused couples therapy
Therapy focused on uncovering emotional problems that harm relationships.
The ability to share or understand other people’s feelings.
endocrine disruptors
Environmental pollutants that have endocrine effects.
The study of glands and hormones.
The lower, innermost layer of embryonic cells, which give rise to the digestive system and lungs.
endometrial cancer
Cancer of the endometrium of the uterus.
The growth of endometrial tissue at abnormal locations such as the oviducts.
The internal lining of the uterus.
The sinking of a fetus’s head into a lower position in the pelvis in preparation for birth. Also called lightening.
A lipid outer membrane possessed by some viruses.
epididymis (pl. epididymides)
A structure, attached to each testis, through which sperm must pass before entering the vas deferens.
Inflammation of the epididymis.
epidural anesthesia
Anesthesia administered just outside the membrane that surrounds the spinal cord.
A cut extending the opening of the vagina backward into the perineum, performed by an obstetrician with the intention of facilitating childbirth or reducing the risk of a perineal tear.
erectile dysfunction
A persistent inability to achieve or maintain an erection sufficient to accomplish a desired sexual behavior such as coitus to orgasm. Earlier known as impotence.
The expansion and stiffening of the clitoris, penis, or nipples in response to sexual stimulation or fantasy.
Sexually themed works, such as books or sculpture, deemed to have literary or artistic merit.
The delusional belief that a sexually desired but unattainable person is actually in love with oneself.
Euphemism for a prostitute who advertises by print, word of mouth, or the Internet.
escort service
A service that provides prostitutes, generally contacted by telephone.
A method of tubal sterilization that blocks the oviducts by use of metal coils.
The principal estrogen, secreted by granulosa cells in ovarian follicles.
Any of a class of steroids—the most important being estradiol—that promote the development of female secondary sexual characteristics at puberty and that have many other functions in both sexes.
The restricted period within the ovarian cycle when females of some species are sexually receptive; “heat.”
The study of a cultural group, often by means of extended individual fieldwork.
An organism whose cells contain nuclei.
A man who has been castrated.
The change in the genetic makeup of living populations over time.
evolutionary psychology
The study of the influence of evolution on mental processes or behavior.
The idea that one nation, race, or species is subject to understandings or rules different from those to which all others are subject.
excitement phase
The beginning phase of the sexual response cycle.
A paraphilia involving exposure of the genitalia to strangers, sometimes with masturbation; also called “flashing.”
exposure therapy
A form of psychotherapy for victims of rape or abuse in which they are encouraged to recall the traumatic event in a safe environment.
extended-use regimen
A regimen of contraceptive pills that allows for fewer or no menstrual periods.
external genitalia
The sexual structures on the outside of the body.
extrafamilial child molester
A person who has had sexual contact with children outside his immediate family.
extra-pair relationship
A sexual relationship in which at least one of the partners is already married to or partnered with someone else.


An imagined experience, sexual or otherwise.
A tough sheet or sheath of connective tissue.
Sexual contact between the mouth of one person and the penis of another.
female circumcision
Any of several forms of ritual cutting or excision of parts of the female genitalia.
female condom
A plastic pouch inserted into the vagina as a contraceptive and/or to prevent disease transmission.
female sexual arousal disorder
Insufficient physiological arousal in women, such as to make sex unpleasurable or painful.
A type of cervical cap that has a raised brim.
The movement to secure equality for women; the study of social and psychological issues from women’s perspectives.
Prejudice against femininity in males.
Feminine-acting, often used to describe certain lesbians or bisexual women.
fertility awareness methods
Contraceptive techniques that rely on avoiding coitus during the woman’s fertile window. Also called rhythm methods or periodic abstinence methods.
The entry of a sperm into an ovum, thus transforming the ovum into a genetically unique diploid organism capable of development (conceptus).
fetal alcohol syndrome
A collection of physical and behavioral symptoms in a child who was exposed to high levels of alcohol as a fetus.
Sexual arousal by inanimate objects, materials, or parts of the body.
The developing organism between the time when the main anatomical structures of the body have been established (in humans, approximately 6 weeks after conception) and birth.
A noncancerous tumor arising from smooth muscle cells of the uterus.
A fringe-like set of extensions from the infundibulum of the oviduct.
first polar body
A small body containing the discarded chromosomes from an oocyte’s first meiotic division.
A whiplike fiber, extending from a spermatozoon or other cell, that confers motility.
fluctuating asymmetry
A difference between the left and right sides of the body that results from random perturbations of development.
An oocyte with its supporting cells within the ovary.
follicle-stimulating hormone (FSH)
One of the two major gonadotropins secreted by the pituitary gland; it promotes maturation of gametes.
follicular phase
The phase of the menstrual cycle during which follicles are developing under the influence of gonadotropins.
Any kind of sexual touching of the partner’s body.
The cerebral hemispheres and basal ganglia.
Sexual behavior engaged in during the early part of a sexual encounter, with the aim of increasing sexual arousal.
The loose skin that partially or completely covers the glans in males who have not been circumcised.
A strip of loose skin on the underside of the penis, running between the glans and the shaft.
A paraphilia involving touching or rubbing the clothed genitals against a stranger without their consent or without their knowledge, as in a crowded public place.
A simple sugar (monosaccharide) present in semen.
functional magnetic resonance imaging (fMRI)
A form of magnetic resonance imaging that maps brain activity by detecting the associated changes in blood flow.


A germ cell (ovum or sperm) that fuses with another to form a new organism.
gamma-hydroxybutyrate (GHB)
A central nervous system depressant that has been used to facilitate rape.
Collections of neurons outside the central nervous system.
Colloquial term for homosexual.
gay bashing
Hate crimes against gay people. Sometimes includes verbal abuse as well as physical violence.
The ability to recognize gay people on the basis of unconscious behaviors, voice quality, gait, and so on.
The collection of psychological traits that differ between males and females.
gender constancy
A child’s understanding that sex is a fixed attribute.
gender dysphoria
The unhappiness caused by discordance between a person’s anatomical sex and gender identity.
gender identity
A person’s subjective sense of being male or female.
gender role
The expression of gender identity in social behavior.
gender schema
A collection of ideas about gender that influences perception and judgment.
Atypical in gender characteristics.
A stretch of DNA that is transcribed as a functional unit; a unit of inheritance.
General Social Survey (GSS)
A long-running periodic survey of the U.S. population run by the National Opinion Research Center.
The study of the mechanisms of inheritance.
genital end-bulbs
Specialized nerve endings, found in the genital area, that probably detect the tactile stimulation associated with sexual activity.
genital herpes
An infection of the genital area caused by HSV-2 or (less commonly) HSV-1.
genital ridges
Two clusters of cells in the embryo that give rise to the gonads.
genital swelling
Regions of the genitalia in the embryo that give rise to the labia majora (in females) or the scrotum (in males).
genital tubercle
A midline swelling in front of the cloaca, which gives rise to the glans of the clitoris (in females) or 
penis (in males).
genital warts
Wartlike growths on or near the genitalia or anus, caused by infection with human papillomavirus.
An organism’s entire complement of DNA, including all its genes. In some viruses, such as HIV, the genome is composed of RNA.
Bearing young in the uterus; pregnancy.
gestational age
A fetus’s age timed from the onset of the mother’s last menstrual period.
gestational surrogate
A woman who carries a pregnancy on behalf of another woman or couple.
A male prostitute who caters to women.
The terminal knob of the clitoris or penis.
A polymer of glucose used for energy storage.
An organ that produces gametes (a testis in males; an ovary in females).
gonadal intersexuality
The existence of ovarian and testicular tissue in the same individual. Also called true hermaphroditism.
A hormone that regulates the function of the gonads.
gonadotropin-releasing hormone (GnRH)
A hormone secreted by the hypothalamus that stimulates the release of gonadotropins from the anterior lobe of the pituitary gland.
A sexually transmitted disease caused by infection with the bacterium Neisseria gonorrhoeae.
Good Lives model
A form of therapy for sex offenders that focuses on improving the subject’s ability to achieve a broad range of life goals.
An HIV glycoprotein that binds to the host cell receptor, CD4.
Gräfenberg spot (G-spot)
A controversial area of increased erotic sensitivity on or deep within the front wall of the vagina.
granulosa cells
Cells within an ovarian follicle that support the oocyte and secrete sex steroids.
granulosa-lutein cells
Cells of the corpus luteum, derived from follicular granulosa cells, that secrete progesterone.
gray matter
A region of the central nervous system containing the cell bodies of neurons.
group marriage
Three or more people living together in a marriage-like relationship.
growth hormone
A protein hormone secreted by the pituitary gland that promotes growth.
grudge stalking
Nonsexual revenge stalking.
Either of two bilateral fibrous bands that are involved in the descent of the gonads in the fetus.
A specific sexual attraction to male-to-female transgenders or transexuals.
Enlargement of one or both breasts in a male.
Sexually attracted to women.


A psychological or physiological process that reduces a person’s response to a stimulus or drug after repeated or prolonged exposure.
Possessing half the usual complement of chromosomes.
Related to explicit pornography, such as images of penetrative sex and ejaculation.
1. The quarters for wives and children in a polygamous Muslim household. 2. In some species, the group of females who live and mate with a single male.
heavy petting
Sexually touching the partner’s genitalia or breasts.
An adult whose sexual attraction is directed mainly to pubescent children.
hepatitis A
Liver disease caused by the hepatitis A virus. It is sometimes transmitted sexually.
hepatitis B
Liver disease caused by the hepatitis B virus, a virus that is often transmitted sexually.
hepatitis viruses
Viruses that cause liver disease.
Capable of being passed down from parent to offspring.
An organism that combines male and female reproductive functions.
Sexually attracted to persons of the opposite sex.
Sexual attraction only (or predominantly) to persons of the other sex.
highly active antiretroviral therapy (HAART)
Combinations of antiretroviral drugs that have proved effective in the treatment or prevention of AIDS.
A member of a class of male-to-female transexuals in northern India and Pakistan.
HIV-symptomatic disease
Health problems caused by HIV, especially those that occur before the criteria for an AIDS diagnosis have been met.
The tendency of sexually partnered couples, or married couples, to resemble each other in a variety of respects.
Prejudice against homosexuality or gay people.
Sexually attracted to persons of one’s own sex.
Sexual attraction only (or predominantly) to persons of one’s own sex.
hooking up
Uncommitted sex with an acquaintance.
hostile-environment harassment
Sexual harassment involving a pattern of conduct that creates an intimidating work environment.
hot flashes (hot flushes)
Episodes of reddening and warmth of the skin associated with menopause.
human chorionic gonadotropin (hCG)
A gonadotropin secreted by the conceptus and by the placenta; it prevents regression of the corpus luteum.
human immunodeficiency virus (HIV)
The retrovirus that causes AIDS.
human papillomavirus (HPV)
Any of a group of viruses that can be sexually transmitted and that cause genital warts or other lesions; some types predispose infected persons to cancer of the cervix or anus.
A male prostitute.
A collection of fluid around a testicle.
A membrane, usually perforated or incomplete, that covers the opening of the vagina. It may be ruptured by first coitus or by other means.
Abnormally high levels of testosterone or other androgens.
Excessive sexual desire or behavior.
hypoactive sexual desire disorder
Low or absent interest in sex, when this condition causes distress. Also called low sexual desire.
Producing insufficient levels of sex hormones.
An abnormal location of the urethral meatus on the underside of the glans, the shaft of the penis, or elsewhere.
A small region at the base of the brain on either side of the third ventricle; it contains cell groups involved in sexual responses and other basic functions.
Surgical removal of the uterus, sometimes along with the ovaries and oviducts.
An abortion performed via a surgical incision in the abdominal wall and the uterus.


Lacking an identifiable cause.
imperforate hymen
A hymen that completely closes the introitus.
An implanted hormonal contraceptive.
implicit association test
A psychological test that is intended to reveal unconscious or unstated preferences.
in vitro fertilization (IVF)
Any of a variety of assisted reproduction techniques in which fertilization takes place outside the body.
(third interstitial nucleus of the anterior hypothalamus) A cell group in the hypothalamus, a part of the brain, that differs in size between men and women and between gay and straight men.
inclusive fitness
The likelihood that an individual’s genes will be represented in future generations, both in direct descendants and in the descendants of close relatives.
incompetent cervix
A weakening and partial opening of the cervix caused by a previous traumatic delivery, surgery, or other factors.
indecent exposure
The crime of exposing the genitals or female breasts in public—exact legal definitions vary.
induced abortion
An abortion performed intentionally by medical or surgical means.
induced labor
Labor induced artificially by drugs.
infant formula
Manufactured breast milk substitute.
Inability (of a man, woman, or couple) to achieve pregnancy.
The most invasive form of female circumcision, involving clitoridectomy plus the sewing together of the labia majora over the vestibule. Also called pharaonic circumcision.
The flared-out portion of the oviduct close to the ovary.
inguinal canal
A short canal passing through the abdominal wall in the region of the groin in males.
A peptide hormone involved in the interaction between the pituitary gland and the gonads as well as in other functions.
An enzyme that inserts viral DNA into the genome of the host cell.
internal fertilization
Fertilization within the body.
A neuron whose connections are local.
interpersonal scripts
Patterns of behavior that develop between couples.
Having a biological sex that is ambiguous or intermediate between male and female.
The sense of connectedness in an established relationship.
intimate partner stalking
Stalking of a current or former spouse or other intimate partner.
intimate partner violence
Violence between sex partners.
intracytoplasmic sperm injection (ICSI)
An assisted reproduction technique in which a single sperm is injected into the cytoplasm of an ovum.
intrafamilial child molester
A person who has had sexual contact with his own children or stepchildren. Also called incest offender.
intrauterine device (IUD)
A device placed in the uterus as a contraceptive.
The entrance to the vagina, usually covered early in life by the hymen.
The commitment or expenditure of resources for a goal, such as reproductive success.
ischiocavernosus muscle
One of the muscles that attach to the internal portions of the penis and clitoris. It assists with erection and (in men) ejaculation.
Estrogen-like compounds of plant origin.
The narrow portion of the oviduct close to the uterus.


Yellowing of the skin and mucous membranes, caused by liver disease.
Fear that a partner may be sexually or emotionally unfaithful.


Male-to-female transgenders in Thailand.
Kegel exercises
Exercises to strengthen pelvic floor muscles, with the aim of improving sexual function or alleviating urinary leakage.
ketamine (“K”)
An anesthetic and recreational drug that has been used to facilitate rape.
kin selection
The theory that it can be advantageous, in evolutionary terms, to support the reproductive success of close relatives.
Kinsey scale
A 7-point scale of sexual orientation devised by Alfred Kinsey.
A hormone produced in the hypothalamus that is involved in the initiation of puberty.
A social panic based on the fear that the penis will retract and disappear, causing death.


labia majora
The outer lips: fleshy skin folds, partially covered in pubic hair, that extend from the mons.
labia minora
The inner lips: hairless, loose folds of skin located between the labia majora and immediately flanking the vestibule.
labioplasty (or labiaplasty)
Plastic surgery on the labia minora, usually to reduce their size.
The process of childbirth.
The production of milk in the mammary glands.
lactiferous sinus
One of the storage areas for milk near the nipple.
Lamaze method
A method of childbirth instruction that focuses on techniques of relaxation and other natural means of pain reduction.
Abdominal surgery, such as tubal sterilization, performed through a small incision with the aid of a laparoscope (a fiber-optic viewing instrument).
latent phase
An asymptomatic phase of syphilis or other infectious disease.
Lea’s shield
A type of diaphragm with a one-way valve.
legalization with regulation
Conversion of an activity such as prostitution from a crime to a governmentally regulated occupation.
A hormone secreted by fat cells that may play a role in triggering puberty.
Homosexual—applied to women only.
Leydig cells
Cells located between the seminiferous tubules in the testis that secrete steroids. Also called interstitial cells.
A subdivision of a gland or other region.
Small subdivisions of an organ, such as the breast.
A bloody vaginal discharge that may continue for a few weeks after childbirth.
locus coeruleus
A nerve center in the pons that helps regulate the state of consciousness.
In female rodents, an inverse arching of the back that exposes the vulva for intromission by a male.
luteal phase
The phase of the menstrual cycle between ovulation and the beginning of menstruation.
luteinizing hormone (LH)
One of the two major gonadotropins secreted by the pituitary gland; it promotes the secretion of androgens and, in females, participates in the regulation of the menstrual cycle.
A contraceptive pill designed for complete elimination of menstrual periods.


The traditional Latino culture of manliness, which delineates sharp gender roles and gives men certain obligations and privileges.
A woman who manages a brothel or an escort service.
A man who took a female gender role in Polynesian society and performed ritual dances.
male condom
A sheath placed over the penis as a contraceptive and/or to prevent disease transmission.
mammary glands
The milk-producing glands within the breasts.
Radiographic inspection of the breasts.
marriage and family counselor
Therapist who assesses or treats interpersonal problems arising between spouses or other intimate partners.
Cause to become male or male-like.
Sexual arousal from being subjected to pain, bondage, or humiliation.
massage parlor
An establishment for massage that may also offer the services of prostitutes.
Surgical removal of a breast.
Inflammation of the breast.
Sexual self-stimulation. Sometimes also used to refer to manual stimulation of another person’s genitalia.
masturbatory reconditioning
A form of behavior therapy that uses the pleasure of orgasm to increase sexual arousal to previously nonarousing targets.
mate guarding
A behavior in which a male animal prevents sexual contact between his mate and other males.
Tracing descent through the female line.
media fetishism
Sexual attraction to materials such as rubber or silk. Also called material fetishism.
medial preoptic area
A region of the hypothalamus involved in the regulation of sexual behaviors typically shown by males.
median eminence
A region of the hypothalamus where GnRH is secreted, located immediately above the pituitary gland.
medical abortion (or medication abortion)
An abortion induced with drugs.
The portion of the brainstem closest to the spinal cord.
A pair of cell divisions that produces haploid gametes.
The onset of menstruation at puberty.
The final cessation of menstruation at the end of a woman’s reproductive years.
menopausal hormone therapy (MHT)
Use of hormones to treat symptoms occurring during or soon after menopause.
Excessively heavy menstrual bleeding.
menstrual cramps
Sharp pelvic pains that may accompany or precede menstruation.
menstrual cup
A cup placed within the vagina that collects the menstrual flow.
menstrual toxic shock syndrome
A rare but life-threatening illness caused by a staphylococcal infection and associated with tampon use.
The breakdown and shedding of the endometrium at approximately monthly intervals, with consequent loss of tissue and blood from the vagina.
The middle layer of embryonic cells, which give rise to bone, muscle, connective tissue, and the cardiovascular system.
A transitory embryonic kidney that provides tissue to the gonads.
A drug used in some medical abortions.
The study of microscopic organisms, especially those that cause disease.
A penis shorter than about 2 cm (0.8 inches) in stretched length at birth.
The region of the brainstem between the pons and the thalamus.
The portion of the tail of a sperm that is closest to the head, containing mitochondria.
A progestin receptor antagonist used to induce abortion. Also known as RU-486.
milk let-down reflex
The ejection of milk into the milk ducts in response to suckling. Also called milk-ejection reflex.
Abdominal surgery, such as tubal sterilization, performed through a short incision.
A hormone-releasing IUD.
A prostaglandin used in medical abortions.
Cell division in which the chromosome number is preserved.
Pain associated with ovulation.
molluscum contagiosum
A skin condition marked by small raised growths; it is caused by a pox virus.
Compounds containing an amine group, including catecholamines and serotonin.
1. Marriage limited to two persons. 2. A sexual relationship in which neither partner has sexual contact with a third party.
mons veneris (mons)
The frontmost component of the vulva: a mound of fatty tissue covering the pubic symphysis.
The conceptus when it consists of about 16 to 32 cells arranged in a compact spherical mass.
motor neuron
A neuron that triggers the contraction of muscle fibers.
A male-typical sexual behavior: climbing onto the female to reach a position in which intromission is possible. (Used mostly for nonhuman animals.)
A surface layer of cells (epithelium) that is lubricated by the secretions of mucous glands.
A thick or slippery secretion.
Müllerian duct
One of two bilateral ducts in the embryo that give rise to the female reproductive tract.
A contract to marry for a fixed period of time.
A change in an organism’s genome.
mutual masturbation
Reciprocal, simultaneous manual stimulation of a partner’s genitals.
A group of very small cellular organisms that may cause urethritis.
The muscular layers of the wall of the uterus.
A general increase in muscle tension.


Naegele’s rule
A traditional rule for the calculation of a pregnant woman’s due date: 9 calendar months plus 1 week after the onset of the last menstrual period.
National Health and Social Life Survey (NHSLS)
A national survey of sexual behavior, relationships, and attitudes in the United States, conducted in the early 1990s.
National Survey of Sexual Attitudes and Lifestyles (NSSAL)
A British survey of sexual behavior, relationships, and attitudes conducted in the early 1990s.
National Survey of Sexual Health and Behavior (NSSHB)
A national survey of sexual behavior in the United States, based at Indiana University and published in 2010.
natural selection
The survival and reproduction of those individuals that are best adapted to their environment.
Kissing or caressing of the head and neck.
A paraphilia involving sexual arousal from viewing or having contact with dead bodies.
An HIV protein whose function is uncertain but which is necessary for the virus to be pathogenic.
negative feedback
A control system in which a compound directly or indirectly lowers its own rate of synthesis or secretion.
neuromuscular junction
A synapse between an axon and a muscle fiber.
A single nerve cell with all its extensions.
The study of the nervous system.
Mental disorders such as depression that, in Freudian theory, are coping strategies against repressed sexual conflicts.
A compound released at a synapse that increases or decreases the excitability of an adjacent neuron.
nitric oxide
A dissolved gas that functions as a neurotransmitter in erectile tissue.
nocturnal emission
Ejaculation during sleep.
nocturnal orgasm
Orgasm during sleep.
nongonococcal urethritis (NGU)
Urethritis not caused by gonorrhea.
nuchal translucency test
The ultrasonographic measurement of the skin fold at the neck of a fetus, useful in the prenatal diagnosis of Down syndrome and other congenital anomalies. Also called nuchal fold test.
nucleus (pl. nuclei)
In neuroanatomy, a recognizable cluster of neurons in the central nervous system.
nucleus accumbens
A nucleus within the basal ganglia that is part of the brain’s reward system.
A contraceptive ring placed in the vagina.


object fetishism (or objectophilia)
Sexual arousal by inanimate objects.
Related to sexually themed publications, art, films, performances, or behavior that is deemed offensive to public morals or that violates legal standards of acceptability.
obsessive–compulsive disorder (OCD)
A mental disorder marked by anxiety, repetitive thoughts or urges, and behaviors that temporarily relieve those urges.
obsessive relational intrusion
Obsessive pursuit of a person by a rejected lover.
Infrequent or irregular menstruation.
Onuf’s nucleus
A sexually dimorphic group of motor neurons in the sacral segments of the spinal cord that innervates striated muscles associated with the penis and clitoris.
A cell capable of developing into an ovum.
oral herpes
Herpes infection of the mouth, caused by HSV-1 or (less commonly) HSV-2.
Surgical removal of one or both testicles.
Inflammation of a testicle.
organizational effect
The influence of a sex hormone on the development of brain circuitry.
The intense, pleasurable sensations at sexual climax, and the physiological processes that accompany them.
orgasmic platform
The outer portion of the vagina and surrounding tissues, which thicken and tense during sexual arousal.
Ortho Evra
A contraceptive patch.
The opening in the cervix that connects the vagina with the cervical canal.
Reduction in the mineral content of bone, predisposing to fractures.
Sexual activities other than coitus, promoted as a means for preventing unwanted pregnancy and reducing the risk of STD transmission.
ovarian cysts
Cysts within the ovary that can arise from a number of different causes.
The female gonad; the organ that produces ova and secretes sex steroids.
Either of two bilateral tubes that lead from the uterus toward the ovaries; the usual site of fertilization. Also called fallopian tube.
Release of an ovum from the ovary.
ovum (pl. ova)
A mature female gamete, prior to or immediately after fertilization.
A hormone secreted by the pituitary gland that stimulates uterine contractions and the secretion of milk.


pair bond
A durable sexual relationship between two individuals.
Pap test
The microscopic examination of a sample of epithelial cells taken from the cervix or (less commonly) the anus.
A copper-containing IUD.
An unusual form of sexual arousal or behavior that is considered to be a psychological problem.
Entrapment of the retracted foreskin behind the corona.
Paralysis affecting the lower half of the body.
parasympathetic nervous system
A division of the autonomic nervous system; among other functions, its activity promotes erection of the penis and clitoris.
paraurethral glands
Glands situated next to the female urethra, thought to be equivalent to the larger prostate gland in males. Also known as Skene’s glands.
Asexual reproduction from an unfertilized ovum; “virgin birth.”
Fetishistic attraction to specific parts of the body.
partible paternity
The belief that two or more men may be fathers of the same child.
Delivery of offspring; childbirth.
The overwhelming feeling of attraction typical of the early stage of a loving relationship.
paternity test
A test to identify an individual’s father by DNA analysis.
Sexual attraction to prepubescent and/or pubescent children.
A person whose sexual feelings are directed mainly toward prepubescent children.
pelvic examination
A visual and digital examination of the vulva and pelvic organs.
pelvic floor
A muscular sling that underlies and supports the pelvic organs.
pelvic inflammatory disease (PID)
An infection of the female reproductive tract, often caused by sexually transmitted organisms.
pelvic nerves
Nerves that convey parasympathetic signals from the lower spinal cord to the genitalia and other organs.
penile bulb
An expansion of the corpus spongiosum at the root of the penis.
penile implant
An implanted device for treatment of erectile dysfunction.
The erectile, erotically sensitive genital organ in males.
A polymer of amino acids, usually shorter than a protein.
perfect-use failure rate
The percentage of women using a contraceptive technique correctly who will become pregnant in a year.
The phase prior to menopause that is marked by irregular menstrual cycles.
The outer covering of the uterus.
The region of skin between the anus and the scrotum or vulva.
peripheral nervous system
The motor and sensory connections between the central nervous system and peripheral structures such as muscles and sense organs.
persistent genital arousal disorder
Long-lasting physiological arousal in women, unaccompanied by subjective arousal or pleasure.
The collection of mental and behavioral traits, especially those related to emotions and attitudes, that characterizes an individual.
An obsolete term for atypical sexual desire or behavior, viewed as a mental disorder.
Sexually touching the partner’s body (often taken to exclude the breasts or genitalia).
Peyronie’s disease
Pathological curvature of the penis.
A volatile compound that is released by one organism and that triggers a specific behavior in another member of the same species.
A tightening of the foreskin, preventing its retraction from the glans.
phone sex
Erotic telephone conversations, usually carried out for pay.
A man who manages prostitutes in exchange for part of their earnings.
pituitary gland
A gland situated below, and under the control of, the hypothalamus; its posterior lobe secretes oxytocin and vasopressin, and its anterior lobe secretes gonadotropins and other hormones.
A vascular organ, partly of fetal and partly of maternal origin, by which gases, nutrients, hormones, and waste products are exchanged between the fetus and its mother.
placenta previa
An abnormally low position of the placenta, so that it partially or completely covers the internal opening of the cervix.
Plan B
A progestin used for emergency contraception.
plateau phase
The phase of the sexual response cycle during which arousal is maintained at a high level.
The formation of nontransient sexual relationships in groups of three or more.
The marriage or mating of one female with more than one male.
polycystic ovary syndrome (PCOS)
A condition marked by excessive secretion of androgens by the ovaries.
Marriage to or (mostly in animals) mating with more than one partner.
The marriage or mating of one male with more than one female.
A common genetic variation between individuals in a species.
A region of the brain above the medulla.
Material (such as art, writing, photographic images, and film) that is intended to be sexually arousing. Also called porn or porno.
post-exposure prophylaxis
A drug treatment designed to prevent establishment of an infection after exposure to a disease agent such as HIV.
post-traumatic stress disorder (PTSD)
A cluster of physical and psychological symptoms that can affect persons who have experienced severe trauma.
postganglionic neuron
A neuron with its cell body in an autonomic ganglion and an axon that innervates glands or smooth muscles in a peripheral organ such as the genitalia.
postmenopausal hormone therapy
Hormone treatment extending for a long time after menopause.
postnuptial agreement
A financial agreement between spouses.
postovulatory phase
An alternative term for luteal phase.
The period after birth.
postpartum depression
Depression in a mother during the postpartum phase.
The age range including the beginning of puberty, approximately from 8 to 12 or from 8 to 13.
preantral follicle
A follicle that has enlarged but does not yet have an antrum.
precocious puberty
Puberty that begins early enough to be considered a medical problem.
preconception care
Medical care and counseling provided to women before they become pregnant.
pre-exposure prophylaxis
A drug taken before exposure to a disease agent to prevent infection.
preganglionic neuron
An autonomic motor neuron in the spinal cord.
The state of carrying a living, implanted conceptus, embryo, or fetus.
preimplantation genetic screening
Testing of in vitro fertilization embryos for genetic defects prior to implantation.
premature birth
Birth that occurs more than 3 weeks before a woman’s due date. Also called preterm birth.
premature ejaculation
Ejaculation before the man wishes, often immediately on commencement of coitus. Also called rapid ejaculation.
premenstrual dysphoric disorder (PMDD)
PMS-associated mood changes that are severe enough to interfere with relationships.
premenstrual syndrome (PMS)
A collection of physical and/or psychological symptoms that may begin a few days before the menstrual period and continue into the period.
prenatal care
Medical care and counseling provided to pregnant women.
prenuptial agreement
A contract signed before marriage, spelling out the disposition of wealth in the event of divorce.
preovulatory follicle
The single, enlarged antral follicle that will ovulate in a particular cycle.
preovulatory phase
An alternative term for follicular phase.
primary amenorrhea
Failure to commence menstruation at puberty.
primary disorder
A disorder that is not preceded by any period of healthy function.
primary oocyte
An oocyte arrested in its first meiotic division.
primary syphilis
The first phase of syphilis, marked by the occurrence of a chancre.
primordial follicle
An undeveloped primary oocyte with its surrounding granulosa cells.
primordial germ cells
The cells that give rise to oocytes and to the progenitors of sperm.
proceptive behavior
Behavior by females that may elicit sexual advances by males.
Believing that abortion should be legal under some or all circumstances.
Production of offspring.
A steroid hormone secreted by the ovary and the placenta; it is necessary for the establishment and maintenance of pregnancy.
progestin (or progestagen)
Any of a class of steroids, the most important being progesterone, that cause the endometrium to proliferate and help maintain pregnancy. (The term progestin is sometimes reserved for synthetic compounds.)
progestin-only pill
An oral contraceptive that contains progestin but no estrogen. Also called the “mini-pill.”
A protein hormone secreted by the anterior lobe of the pituitary gland that promotes breast development, among other effects.
The slipping out of place of an organ, such as the uterus.
Opposed to abortion; believing that abortion should be illegal under most or all circumstances.
Engaging in numerous casual or short-lived sexual relationships.
pronucleus (pl. pronuclei)
A nucleus containing a haploid set of chromosomes derived from a sperm or ovum.
prostaglandin E1 (alprostadil)
A hormone that is injected into the penis to produce an erection.
A group of nonsteroidal signaling molecules that, among many other functions, help prepare the uterus for childbirth.
prostate cancer
Cancer of the prostate gland.
prostate gland
A single gland at the base of the bladder, surrounding the urethra; its secretions are a component of semen.
prostate-specific antigen (PSA)
An enzyme secreted by the prostate gland; its presence at high levels in the blood is suggestive of, but not diagnostic of, prostate cancer.
Inflammation of the prostate gland; may be acute or chronic.
The practice of engaging in sex for pay.
An enzyme that cuts proteins at specific locations.
A long polymer made up of amino acids.
Outdated term for intersexed conditions involving structures other than the gonads.
The study of the biological bases of mental processes and behavior.
psychological anthropology
The study of the interaction of cultural and mental processes.
The study of mental processes and behavior.
The biological transition to sexual maturity.
pubic hair
Hair that appears on portions of the external genitalia in both sexes at puberty.
pubic lice
Insects (Phthirus pubis) that preferentially infest the pubic region.
pubic symphysis
The junction of the left and right pubic bones, the frontmost elements of the pelvic skeleton.
pubococcygeus muscle
A pair of muscles in the pelvic floor that form a sling around the vagina.
pudendal nerves
Peripheral nerves supplying the external genitalia.


Paralysis affecting almost the entire body below the neck.
The onset of movements by the fetus that can be felt by the mother.
quid pro quo harassment
Unwelcome sexual advances, usually made to a worker in a subordinate position, accompanied by promises or threats.
Hispanic coming-of-age ceremony for girls.


radical prostatectomy
Surgical removal of the entire prostate gland and local lymph nodes.
Coitus (and sometimes other penetrative sex acts) accomplished by force or the threat of force.
rape shield laws
Laws that protect rape victims, for example, by limiting the introduction of evidence about their prior sexual behavior.
rape trauma syndrome
A cluster of persistent physical and psychological symptoms seen in rape victims; comparable to post-traumatic stress disorder.
The midline ridge of the perineum.
real-life experience
A period of living in the role of the other sex as a prelude to sex reassignment.
A molecular structure to which a hormone or neuro-transmitter binds. Upon binding, the receptor triggers a specific cellular activity.
recessive trait
An inherited trait that shows itself only when the responsible gene is present on both homologous chromosomes.
The tendency of convicted offenders to reoffend.
The final, straight portion of the large bowel. It connects to the exterior via the anus.
Red Queen hypothesis
The idea that sexual reproduction is advantageous because it helps defend organisms against parasites.
refractory period
In males, a period of reduced or absent sexual arousability after orgasm.
relapse prevention therapy
Therapy aimed at training a person to avoid or cope with situations that trigger the undesirable behavior.
reportable disease
A disease, cases of which must by law be reported to health authorities.
reproductive physiology
The study of fertility and pregnancy.
reproductive tract
The internal anatomical structures in either sex that form the pathway taken by gametes or the conceptus.
resolution phase
The phase of the sexual response cycle during which physiological arousal subsides.
rete testis
A network of spaces, between the testis and epididymis, through which sperm must pass.
An RNA virus whose genome is transcribed into DNA within the host cell.
An HIV protein that triggers production of viral RNA in a form suitable for export from the cell.
reverse transcriptase
An enzyme produced by a retrovirus that transcribes viral RNA into DNA.
Rh factor
An antigen on the surface of red blood cells that, when present in a fetus but not in its mother, may trigger an immune response by the mother, resulting in life-threatening anemia of the fetus or newborn.
A tranquilizer that has been used to facilitate rape.
German measles, a viral infection that can cause developmental defects in fetuses whose mothers contract the disease during pregnancy.


Sexual arousal by the infliction of pain, bondage, or humiliation on others, or by witnessing the recipient’s suffering.
sadomasochism (S/M)
The infliction and acceptance of pain or humiliation as a means of sexual arousal.
saline-induced abortion
An abortion induced by use of a strong salt solution.
Infestation with a mite (Sarcoptes scabiei) that burrows within the skin.
script theory
The analysis of sexual and other behaviors as the enactment of socially instilled roles.
The sac behind the penis that contains the testicles.
An extended-use contraceptive pill.
An extended-use contraceptive pill.
sebaceous glands
Oil-secreting glands associated with hair follicles.
second polar body
A small body containing the chromosomes discarded during the second meiotic division of an ovum.
secondary amenorrhea
Absence of menstruation in a woman who has previously menstruated normally.
secondary disorder
A disorder that follows some period of healthy function.
secondary oocyte
The oocyte in a preovulatory follicle after it has completed its first meiotic division.
secondary sexual characteristics
Anatomical characteristics, such as breasts and facial hair, that generally differ between the sexes but are not used to define an individual’s sex.
secondary syphilis
The second phase of syphilis, marked by a rash and fever.
selective serotonin reuptake inhibitors (SSRIs)
A class of drugs, including antidepressants such as Prozac, that depress sexual function.
The fluid, containing sperm and a variety of chemical compounds, that is discharged from the penis (ejaculated) at the male sexual climax.
A protein secreted by the seminal vesicles that coagulates after ejaculation.
seminal nurture
The belief that multiple acts of coitus promote fetal development.
seminal plasma
The noncellular constituents of semen.
seminal vesicles
Two glands situated to either side of the prostate; their secretions are a component of semen.
seminiferous tubules
Convoluted microscopic tubes within the testis; the site of spermatogenesis.
sensate focus
A form of sex therapy that involves graduated touching exercises.
sensitive period
A period of development during which the survival or growth of a biological system depends on the presence of some factor, such as a hormone.
serial monogamy
Engagement in a series of monogamous relationships.
The change from negative to positive on an antibody test, such as occurs a few weeks or months after HIV infection.
A monoamine derived from the amino acid tryptophan that functions as a neurotransmitter.
Sertoli cell
A type of cell within the seminiferous tubules that nurtures developing sperm and secretes hormones.
sex chromosome
Either of a pair of chromosomes (X or Y in mammals) that differ between the sexes.
sex determination
The biological mechanism that determines whether an organism will develop as a male or a female.
sex hormones
Chemical messengers that influence sexual and reproductive processes.
sex play
A variety of playful activities that add pleasure to sexual interactions.
sex research
The scientific study of sex.
sex steroid
Any of the steroid hormones that are active in sexual and reproductive physiology.
sex therapist
A person who treats sexual disorders, usually by means of psychotherapy and sexual exercises.
sex trader
A person who exchanges sex for money, drugs, or other benefits; a broader term than prostitute.
sex worker
A person who engages in prostitution, pornography, or another sex-related occupation.
sex-reassignment surgery
Surgery to change a person’s genitals or other sexual characteristics.
prejudice or discrimination directed against one sex—usually women.
The scientific study of sex, especially of sexual dysfunctions.
Sending nude or sexually explicit photographs of oneself via mobile phone.
sexual addiction
The idea that a person may be addicted to certain forms of sexual behavior by a mechanism similar to that of substance addiction.
sexual assault
Coercive or nonconsensual sexual contact: a broader category of behaviors than rape.
sexual dimorphism
An anatomical difference between the sexes.
sexual harassment
Unwanted sexual advances or other intimidating sexual behavior, usually in the workplace.
sexual intercourse
Sexual contact, usually understood to involve coitus.
sexual jealousy
Fear that one’s partner is engaging in sexual contacts with another person.
sexual monogamy
A sexually exclusive pair bond.
sexual orientation
The direction of a person’s sexual feelings toward persons of the same sex, the other sex, or both sexes.
sexual reproduction
Reproduction in which the offspring inherit genes from two parents.
sexual response cycle
The sequence of physiological processes that accompany sexual behavior.
sexual sadism disorder
Sexual arousal by the suffering of others, viewed as a paraphilia.
sexual scripts
Socially negotiated roles that govern sexual behavior.
sexual selection
The evolution of traits under the pressure of competition for mates or of choice by mates.
The feelings, behaviors, and identities associated with sex.
sexually dimorphic nucleus of the preoptic area (SDN-POA)
A cell group in the medial preoptic area of the hypothalamus of rodents that is larger in males than in females.
sexually explicit materials
A nonjudgmental phrase denoting pornography.
A vascular space, such as within erectile tissue, capable of being expanded by filling with blood.
situational disorder
A disorder that appears only in certain circumstances.
A whitish, greasy secretion that builds up under the prepuce of the penis or clitoris.
smooth muscle
Muscular tissue that has no microscopic striations. Its contraction is usually involuntary and under the control of the autonomic nervous system.
social monogamy
A pair bond that is not sexually exclusive.
social psychology
The study of our relationship to others.
The effect of social influences such as family, education, peer groups, and the media on the development of psychological or behavioral traits.
The scientific study of society.
Obsolete term for anal sex, or for any homosexual contact. As a legal term it may refer to a variety of prohibited sex acts.
Related to relatively nonexplicit pornography.
The elimination of connective tissue from the cervix, allowing it to thin out and dilate during labor. Also called ripening.
A male gamete, produced in the testis.
sperm bank
A facility that collects, stores, and provides semen for artificial insemination.
spermatic cord
Either of two bilateral bundles of structures, including the vas deferens, blood vessels, and the cremaster muscle, that pass through the inguinal canal to the testis.
The production of sperm.
spermatozoon (pl. spermatozoa)
A male gamete, produced in the testis.
A chemical that kills sperm, available as a contraceptive in a variety of forms, such as foams, creams, and suppositories.
A circular muscle around an orifice whose contraction closes the orifice.
spina bifida
A congenital malformation caused by incomplete closure of the neural tube.
spinal cord
The portion of the central nervous system within the vertebral column.
spinal reflex
A reflex mediated by neurons in the spinal cord, requiring no participation by the brain.
spiral arteries
The arteries that supply blood to the endometrium.
Any of a class of corkscrew-shaped bacteria, including the agent that causes syphilis.
SRY (Sex-determining Region of the Y chromosome)
A gene located on the Y chromosome that causes the embryo to develop as a male.
Obsessive pursuit of a previous, current, or desired sex partner in such a way as to put that person in a state of fear.
standard days method
A simplified calendar method of contraception usable by women with regular cycles.
status orgasmus
An orgasm or uninterrupted sequence of orgasms that last from 20 seconds up to a minute or more.
statutory rape
Penetrative sex when a partner is legally unable to give consent on account of young age, intellectual disability, or unconsciousness.
A surgical procedure to eliminate fertility in either sex.
stop-start method
A sex therapy technique for the treatment of premature ejaculation that involves alternating between stimulating and not stimulating the penis.
Colloquial term for heterosexual.
striated muscle
Muscular tissue that has microscopic striations. Its contraction is usually under voluntary control.
Difficulty in establishing a pregnancy; arbitrarily defined as the absence of pregnancy after a couple has had frequent unprotected sex for 12 months.
A form of male circumcision in which a cut is made along the underside of the penis, exposing the urethra.
A person who is seeking to establish a romantic relationship with another.
Female circumcision limited to incision or removal of the clitoral hood.
An unusual form of male circumcision in which the upper part of the foreskin is incised but not removed.
A protein that lowers surface tension in the lung, allowing inflation with air.
surgical abortion
An abortion induced by a surgical procedure.
suspensory ligament
A ligament that connects the root of the penis to the pubic symphysis.
Couples who agree to engage in casual sexual contacts with others.
sympathetic nervous system
A division of the autonomic nervous system; among other functions, its activity inhibits penile erection but helps trigger ejaculation.
sympto-thermal method
A rhythm method of contraception that uses the measurement of basal body temperature and the testing of cervical mucus to determine the time of ovulation and the fertile window.
A junction where signals are transmitted between neurons or from neurons to muscle fibers.
synaptic cleft
The narrow space between two neurons at a synapse.
A sexually transmitted disease caused by a spirochete, Treponema pallidum.


An HIV protein that promotes the production of viral RNA.
telephone scatalogia
Sexual arousal from making obscene telephone calls.
tertiary syphilis
The third phase of syphilis, marked by multiple organ damage.
testicle or testis (pl. testes)
The male gonad: one of the two glands within the scrotum that produce sperm and secrete sex steroids.
testicular torsion
Twisting of a testicle that cuts off its blood supply.
The principal androgen, synthesized in the testes and, in lesser amounts, in the ovaries and adrenal glands.
The uppermost region of the brainstem.
thecal cells
Cells located on the periphery of an ovarian follicle that synthesize sex steroids.
theca-lutein cells
Cells of the corpus luteum, derived from follicular thecal cells, that synthesize testosterone.
therapeutic abortion
An abortion performed to safeguard a woman’s life or health.
third interstitial nucleus of the anterior hypothalamus (INAH3)
A sexually dimorphic cell group in the medial preoptic area of the human hypothalamus.
Connective tissue partitions separating the sinusoids of erectile tissue.
trans man (or transman)
A female-to-male transexual.
trans woman (or transwoman)
A male-to-female transexual.
transexual (or transsexual)
A person who identifies with the other sex and who seeks to transition to the other sex by means of hormone treatment and sex reassignment surgery. Transexuals can be male-to-female (M-to-F) or female-to-male (F-to-M).
Having a gender identity that is discordant with one’s anatomical sex.
The final phase of dilation of the cervix during labor.
Changing one’s physical sex and social gender.
transnational trafficking of women
Transportation of women from one country to another, usually for purposes of prostitution.
Wearing clothes of the other sex for purposes of sexual arousal. Sometimes applied to cross-dressing for any reason.
Sexual behavior between two women, who lie front to front and stimulate each other’s vulvas with thrusting motions.
Infection with the protozoan Trichomonas vaginalis.
One of three 3-month divisions of pregnancy.
triphasic combination pill
An oral contraceptive regimen that varies the doses of estrogens and progestins around the menstrual cycle.
true hermaphroditism
Outdated term for gonadal intersexuality.
tubal ligation
Female sterilization by tying off the oviducts.
tubal sterilization
A female sterilization technique that involves cutting, cauterizing, or tying off the oviducts. Also called tubal ligation.
tunica albuginea
A fibrous capsule surrounding the corpora cavernosa.
two-spirit person
In Native American cultures, a person with the spirit of both a man and a woman; a transgender person. Also called berdache.
typical-use failure rate
The percentage of women using a contraceptive technique with a typical degree of care who will become pregnant in a year.


ultrasound scan
An imaging procedure that depends on the reflection of ultrasonic waves from density boundaries within the body. Also called ultrasonographic scan.
umbilical cord
The vascular cord that runs from the umbilicus (navel) of the fetus to the placenta.
underage pornography
Pornography involving models or actors who are minors.
unrequited love
Love that is not reciprocated.
The canal that conveys urine from the bladder to the urethral opening. It also serves for the discharge of ejaculatory fluids, if they are present.
urethral folds
Folds of ectodermal tissue in the embryo that give rise to the labia minora (in females) or the shaft of the penis (in males).
urethral meatus
The opening at the tip of the penis (in males) or in front of the vagina (in females).
Inflammation of the urethra, usually caused by an infection.
urogenital sinus
The common opening of the urinary and genital systems in the embryo.
The womb; a pear-shaped region of the female reproductive tract through which sperm are transported and where the conceptus implants and develops.


vacuum aspiration
An abortion procedure in which the conceptus is destroyed and removed by suction.
vacuum constriction system
A device for treating erectile dysfunction that creates a partial vacuum around the penis, thus drawing blood into the erectile tissue.
A muscular tube extending 8–10 cm from the vestibule to the uterine cervix.
vaginal dilator
A plastic cylinder used to enlarge the vagina or to counteract vaginismus.
Inability to experience coitus due to spasm of the muscles surrounding the outer vagina combined with pain or fear of pain.
vagus nerve
The tenth cranial nerve, whose branches innervate the internal organs.
Enlargement of the veins that drain the testis.
vas deferens (pl. vasa deferentia)
Either of the two bilateral ducts that convey sperm from the epididymis to the ejaculatory duct.
A male sterilization techniques that involves cutting or tying off the vasa deferentia.
Tissue swelling caused by increased filling of local blood vessels.
vasomotor control
The physiological regulation of peripheral blood flow.
Surgery to reverse a vasectomy.
venereal disease
Obsolete term for a sexually transmitted disease.
ventral horn
The portion of the gray matter of the spinal cord nearer to the front of the body, where motor neurons are located.
ventral root
A bundle of motor axons that leaves a ventral horn of the spinal cord.
vestibular bulbs
Erectile structures beneath the labia minora, on either side of the vestibule.
The potential space between the left and right labia minora.
An electrically powered vibrating device used to provide sexual stimulation.
An extremely small infectious agent. When not inside a host cell, viruses are metabolically inert but infectious.
A paraphilia involving spying on persons while they are undressing, naked, or engaged in sex.
An HIV protein involved in movement of viral DNA into the host cell nucleus.
The female external genitalia.
vulvar vestibulitis syndrome
A form of dyspareunia marked by inflammation of the vestibule and increased tension in pelvic floor muscles.


waist-to-hip ratio (WHR)
The ratio of the circumference of the body at the waist to the circumference at the hip.
Progressive and extreme loss of body weight.
wet nurse
A woman who breast-feeds someone else’s infant.
white matter
A region of the central nervous system that contains bundles of axons but no neuronal cell bodies.
Obsolete or slang term for a brothel.
withdrawal method
A method of contraception in which the man withdraws his penis from the vagina prior to ejaculation.
Wolffian duct
One of two bilateral ducts in the embryo that give rise to the male reproductive tract.


X chromosome
A sex chromosome that is present as two copies in females and one copy in males.


Y chromosomes
A sex chromosome that is present only in males.
yolk sac
A transient, early extraembryonic structure; the source of primordial germ cells.


zona pellucida
The capsule surrounding an ovum that must be penetrated by the fertilizing sperm.
A persistent preference for sexual contacts with animals, considered as a paraphilia.
A cell formed by the fusion of gametes: a fertilized ovum.