Abbreviation for "below cleavage." When a girl wears a shirt just long enough to cover the nip and the lower part of her boobs are out for some air. Usually, this is only seen in magazines... If you see this in person, you are very fortunate.
Oh my god... Look at her bovage! I love it when girls wear those shirts and let 'em hang out the bottom... If she reaches to grab anything high, the bovage is on our side!