Commonly expressed as the acronym: RAC

1) The visible outline of a girl's ass created when she wearing

leggings with either a long shirt or short dress/skirt that showcases the bottoms of her cheeks where they meet the back of her thighs. Resulting in upside-down cleavage of the ass best appreciated when she's walking up stairs.

2) Summertime variation would include the same get up sans leggings and/or with short-shorts.