Sexual intercourse

From Voyeurweb's Wiki

Two or more persons enjoying sex with each other. Sexual intercourse is defined as any sexually insertive behavior using the penis. It can be anal, oral or vaginal. Typically, when the phrase "sexual intercourse" is used, the common assumption is that a man inserted his penis into a woman's vagina.

If one person enjoys sex with himself or herself, it is called masturbation. Obviously, in this case there can be no sexual intercourse (except for that one guy I saw in a movie back in college)