The groove between one's buttocks, sometimes visible if the person bends over too far, or if his/her pants/shorts are too short/loose. Unlike a buxom girl's chest-cleavage, a sumptuous-sized endowment "back there" is not an alluring feature, as a girl is considered **more** attractive/desirable if she has a **small** cute round rump.

When you eat dirt for the first time and leave your family to build a shack in the woods