The top part of a nice round booty where the full butt cheeks meet the small of the back. It must jut out and fill a booty-loving man's heart with passionate desire.

The bottom part of a nice ass where the butt meets the leg. There is definetly a crease. People with elongated asses that blend into their thighs don't have one.

butt shelf: an implant into a girl's ass that is so high and large you can place a drink on it.

(n) An ass so large as to simulate a shelf, table, nightstand, or other flat tabular object that one might set a drink, ash tray, plates, a TV, or what not on.

A large butt on an otherwise not large woman. So oddly large that it protrudes like a shelf.

a bum that sticks out i.e like a shelf.