PB meaning in Community ?

In human sexuality, top, bottom, and versatile are sex positions or roles during sexual activity, especially between two men. A top is usually a person who penetrates, a bottom is usually one who receives penetration, and someone who is versatile engages in either or both roles. These terms may be elements of self-identity that indicate an individual's usual preference and habits, but might also describe broader sexual identities and social roles.

The terms top and bottom are often used as verbs for the person's actions. The terms do not refer to the literal physical position during sex.