A sex position is a position of the body that people use for sexual intercourse or other sexual activities. Sexual acts are generally described by the positions the participants adopt in order to perform those acts. Though sexual intercourse generally involves penetration of the body of one person by another, sex positions commonly involve penetrative or non-penetrative sexual activities. Three categories of sexual intercourse are commonly practiced: vaginal intercourse involving vaginal penetration , anal penetration , and oral sex especially mouth-on-genital stimulation. The act may also involve anilingus.