A large mass of pubic hair that serves to cushion the base of your penis from the impact of the woman's vagina you are destroying. It may also tickle her labia, which, depending on her preferences, may increase pleasure.
Mike: "I totally annihilated my girlfriend last night."
Ted: "Aren't you sore?"
Mike: "Nah, my bush cush softened the blows."
Ted: "Gross."