People define "sex" in different ways. Some people believe that it only counts as sex if a penis goes into a vagina, but this isn't true for everybody. There are lots of different ideas about what sex can be:

Intercourse: is the insertion of erect penis into the vagina or anus. It may also be used to describe other forms of sexual activity, such as interfemoral intercourse, oral intercourse, or mammary intercourse.

Oral Sex

Cunnilingus: is the stimulation of the external genitalias of the woman with lips, mouth, or tongue. This practice may or may not be continued to orgasm.

Fellatio; is the stimulation of penis using the lips, mouth, or tongue. This practice may or may not be continued to orgasm, and the partner may or may not swallow the ejaculate.

Anal sex: is the sexual activity characterized by anal stimulation or penetration of anus  with various devices including finger, penis, lips, mouth, tongue or objects.

Analingus: is the oral stimulation of the anal area.

Autofellatio: a fellatio performed on oneself.

Axillary intercourse: is the insertion of penis under the armpit.

Interfemoral intercourse: refers to the act of inserting and moving the penis between the thighs.

Mammary intercourse: refers to the insertion and movement of the penis between the breasts.

Body rubbing (dry humping) means rubbing bodies together , especially sexual organs, sometimes leading to orgasm.

Oral-genital sex: is the stimulation of the genital organs using the mouth.

Mutual masturbation: is the sexual activity in which partners stimulate each other’s genitals with hands or sex toys. Sometimes used to refer to a couple watching each other masturbate.

Fisting: is the insertion of a hand into the rectum or vagina of a sexual partner , forming a fist during or after insertion.

Frottage: is the sexual arousal achieved by rubbing against another person , particularly by rubbing against a stranger  in a public place.

Celibacy: is abstinence from all sexual relations, especially for religious reasons.

Masochism: refers to the sexual arousal or orgasm depends on receiving punishment, discipline, humiliation, or servitude.

Nocturnal emissions: are the normal discharges of semen through the penis occurring during the night as a result of erotic dreams. They are also referred to as wet dreams. They are quite natural phenomena that bring no physical or mental harm. Wet dreams are common also amongst girls. Erotic dreams as a result of sexual desire may lead to orgasm during sleep.