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.
by americano May 26, 2003
where someone has been farting in one room for hours on end, and when someone walks in the they get slapped in the face wit the wall of ass.
by smelly ass August 24, 2009