As first mentioned by Patrick from "Spongebob," It is the act of a woman allowing a man to engage in anal pleasures. Usually given in exchange for an invitation to an occasion involving getting dressed up or fancy dinners (i.e. Fraternity formals, Proms).
Tim: "she has been bugging me for a week to let her be my date to formal next week. But if she wants to go, she's going to have to let me get some wumbo action in so there is something in for both of us."