The portion of the female body where the thigh meets the ass. The roundness of the ass creates a crease, similar to cleavage. The rounder the ass, the more pronounced the theavage.
"I was stretching with Alyssa before our soccer game. When she leaned back, I could see right up her athletic shorts to her theavage."
"I was waiting on the stair stepper at the gym and some girl's shorts were so short that I could see her theavage."