AIDS Acquired Immune Deficiency Syndrome, a group of illnesses and conditions affecting people infected with the human immunodeficiency virus (HIV). People may not develop AIDS for several years after being infected with HIV, but they can pass the virus to others. AIDS is life threatening and there is no cure.
Anal sex When a man inserts his penis into the anus of his partner, who can be a man or a woman.
Anus The entrance into the rectum or back passage of the body, which faeces pass through.
Aphrodisiac A substance which is said to increase sex drive or sexual performance. There is no scientific proof that any aphrodisiacs work. Many are harmless but some can be dangerous.
Bisexual Someone who is sexually attracted to both men and women.
Ejaculation When a man reaches orgasm, or 'comes'. White fluid (semen) passes out of the end of his penis.
Genitals Male or female sexual organs.
Heterosexual Someone who is sexually attracted to people of the opposite sex. (A heterosexual, or 'straight', man is attracted to women.)
HIV Human Immunodeficiency Virus, the virus which can lead to a number of illnesses and conditions, known as AIDS. HIV is transmitted through sex, blood (such as through blood transfusions or sharing injecting drug equipment), or from mother to child before or during birth or through breastmilk. HIV can be easily transmitted through unprotected, penetrative sex. However, condoms and safer sex methods can reduce the risk of transmission.
Homosexual Someone who is sexually attracted to people of the same sex. (A homosexual, or 'gay', man is attracted to other men.)
Infertility Not being physically able to have children. Infertility can happen to men and women. Some men use sterilisation, which makes them infertile, as a contraceptive method (see 'Vasectomy').
Intercourse See 'Sexual intercourse'.
Masculinity The feelings and qualities associated with being a man.
Masturbation When a person touches his or her own genitals for pleasure.
Mutual masturbation When two people use their hands to rub or stroke each other's genitals.
Oral sex Contact between one person's mouth and another person's genitals. This can mean licking, kissing or sucking.
Penetration When a man's penis is inside the vagina or anus of a woman or the anus of another man.
Penetrative sex Sex that involves a man's penis being inside his partner's vagina or rectum.
Puberty The age at which boys' and girls' bodies develop into women's and men's bodies and when they become capable of having children. Puberty usually starts between the ages of 9 and 12 and continues until 16 to 18 years.
Rectum The back passage of the body, which is penetrated during anal sex.
Reproductive tract infection (RTI) An infection of the reproductive organs, which may be transmitted by vaginal sex, or bacterial infections that result from changes in the body or illness.
Safer sex Sex with a reduced risk of infections being transmitted. Sex is safer if semen, vaginal fluids and blood are not exchanged between partners. Safer sex includes sex that does not involve penetration, or penetrative sex using a condom. Oral sex is safer than unprotected sexual intercourse. Other forms of contact, such as hugging, stroking or rubbing, carry no risk of HIV or STI transmission.
Sex drive The desire for sex or the urge to have sex.
Sexual intercourse Sexual activity in which a man's penis penetrates a vagina or rectum.
Sexual orientation Whether a person is sexually attracted to people of the same sex, the opposite sex or both sexes.
Sexuality A person's sexual feelings and qualities, often connected with sexual identity or sexual orientation.
Sexually transmitted infection (STI) or sexually transmitted disease (STD) An infection transmitted during vaginal, anal or oral sex.
Sterilisation See 'Vasectomy'.
Unsafe sex Sex with a risk of infections being transmitted. Unsafe sex includes penetrative sex without a condom, unless both partners are sure that they have no infections.
Vasectomy An operation to make men infertile. It involves cutting the vas deferens (the tube that passes semen from the testicles) to prevent sperm being released into the semen.