Those perfectly defined butt cheeks with the crease at the bottom. So the cheek pouches over the crease creating a "fold over bun". This creates a religeous effect when the woman is viewed from behind, while standing, from bun level.
A ball fold over is where the base of your penis meets your scrotum. You can't see the ball fold-over because hidden by the cock.
"I totally got some lint on my ball fold-over the other day"
"I like it when she performs oral sex on my ball fold-over"
"mmmmm mmmm....mmmmMMMMMM"
"My ball fold-over is sore from gyrating"
A prank in which the prankster, in a public restroom, poops into a newspaper, folds it back up, and leaves it in the stall or "bay" for a future occupant. The future occupant then picks up the paper after settling in, and opens it to find human excrement.