When a woman wears a low cut blouse and you can see her breasts, it's called cleavage. When someone similarly exposes her butt cheeks or butt crack, it's called beavage. Example: Check out her beavage. Definitely needs some toning before she wears those shorts again.
BEAVAGE
Meaning of BEAVAGE in English
Slang English vocab. Английский сленговый словарь. 2012