This biological phenomenon occurs just distal to the butt cheeks in wide-hipped women. Where the thigh meets the cheek at the crease, a fold of skin/fat will poke out laterally from the lower outside cheek. When this occurs, it resembles the corner of a mouth of someone who has a chaw of tobacco in their cheek, hence the name chee-chaw. It is typically more visable when said female is wearing tight pants. Chee-chaws will alternate from side to side as the woman steps.
That girl over there has chee-chaws. When she walks it looks like her butt is winking at me.