Vaginal sexual intercourse, also called coitus, is the human form of copulation. While a purpose and effect is reproduction, it is often performed exclusively for pleasure and/or as an expression of love and emotional intimacy. Sexual intercourse typically plays a powerful bonding role; in many societies it is normal for couples to have frequent intercourse while using birth control, sharing pleasure and strengthening their emotional bond through sex even though they are deliberately avoiding pregnancy.
Sexual intercourse may also be defined as referring to other forms of insertive sexual behavior, such as oral sex and anal intercourse.
Sexual intercourse may be preceded by foreplay, which leads to sexual arousal of the partners, resulting in the erection of the penis and natural lubrication of the vagina.
To engage in coitus, the erect penis is inserted into the vagina and one or both of the partners move their hips to move the penis backward and forward inside the vagina to cause friction, typically without fully removing the penis. In this way, they stimulate themselves and each other, often continuing until orgasm in either or both partners is achieved.
During ejaculation, which usually accompanies male orgasm, a series of muscular contractions delivers semen containing male gametes known as sperm cells or spermatozoa from the penis into the vagina.
