when a person's buttocks, usually a female's, does not curve at all. the ass region looks more like an extension of the back with a crack in the middle to allow for waste production. this flat appearance resembles a wall of ass.
Oh man, I put my hands down that chick's pants and it was total wall ass for miles.
ayon kay americano ika-26 ng Mayo, 2003
a person with the ass the size of a wall
ur such a wallass! cuz ur ass is huge
ayon kay Essen ika-09 ng Mayo, 2005