The overwhelmingly horrifying deformation that occurs when a man or woman is so incredibly fat that their lower back forms an entirely separate set of ass cheeks above the normal ones, thus leading to the appearance of having another ass resting on top of the real one.
Holy sh*t dude, look at that chick's quadra-ass! That's f*cking horrible! It's so saggy!!
Yeah, I bet she hides chicken under the top ass cheeks.