Top, bottom and versatile
From The Art and Popular Culture Encyclopedia
The terms top, bottom and switch are used by many people, including heterosexual and LGBT people, BDSM practitioners, and others in regards to sexual activities. For example, the act of pegging involves a female top and a male bottom. Interpretation of these terms may vary across subcultures, or even between different individuals within the same subculture.
These terms may be used simply to describe roles for the duration of a sexual act, or may be used more broadly as a psychological, social, and sexual identity, as well as indicating one's usual preference.