Sexual intercourse
Broadly speaking, the term sexual intercourse may refer to any sexual activities between people, but it is commonly confined to the meaning of coitus (insertion of the erect penis into the vagina). Given this definition, unlike some other sexual activities, sexual intercourse can therefore only be performed by a mixed-sex couple (a man and a woman). Sexual intercourse and masturbation are the two commonest human sexual activities.
Sexual intercourse is usually preceded by foreplay which leads to sexual arousal of the partners, resulting in erection of the penis and moisturization of the vagina. The erect penis is inserted into the vagina and moved back and forth. This often leads to ejaculation and orgasm. Sexual intercourse may be performed in a wide variety of positions, the most common being
- the woman lying on her back, the man on top and facing her ("missionary")
- the woman on hands and knees, the man kneeling behind her (ferarum or "doggy style")
- the man on his back, the woman sitting on top.
- both partners lying on their sides, the man entering from behind.
Various positions have been designated by various societies as "proper" and "improper."
Unlike some other sexual activities, sexual intercourse itself has rarely been tabooed on religious grounds (there have been exceptions) or by government authorities. Indeed, in some societies coitus has been the only "acceptable" sexual activity. On the other hand, relatively strict designations of "appropriate" and "inappropriate" sexual intercourse (wrong person, wrong time, wrong position, etc.) have been almost universal in human societies.
Sexual intercourse with a person without their legal consent (because they have been coerced by force, because they are too young to give informed legal consent, because they are intoxicated, etc.) is called rape and is a serious crime in most jurisdictions.
Sexual intercourse, or coitus, is the basic reproductive method of Homo sapiens as of all mammals and should always be considered likely to result in pregnancy unless adequate contraceptive (birth control) measures are in force. Coitus interruptus, or "withdrawal" of the penis from the vagina just before the man's orgasm, cannot be considered an effective method of contraception (birth control) and is not recommended.
Sexual intercourse, and other sexual activities which involve the transfer of body fluids, are also an effective means of propagating sexually transmitted diseases. Health care professionals suggest that condoms should be used to lessen the risk of contracting STDs, but they should by no means be considered an absolute safeguard. The best suggestion is to avoid sexual intercourse with anyone known to have a sexually transmissable disease, and, indeed, with anyone whose disease-negative status is in doubt.