A depression in the cushion of a couch or chair formed by many hours of sitting. First known usage by Homer Simpson.
Don't sit in my ass groove! You'll mess it up.
ayon kay kelly ika-12 ng Setyembre, 2003
See Butt Marks
Ass grooves were left from sitting on the coach all day.
ayon kay dwayne ika-12 ng Mayo, 2004