"bust" is another word for "upper torso". It seems the woman is unbuttoning her clothes to reveal more of her torso area, possibly too attract the attention of males, or maybe because she is very warm.

Its usually "bust a move" and where i grew up it means that you're encouraging someone to dance.

Never heard of just 'Bust move!'....but... To 'bust a move' means to show a good example of a physical activity, or skill often dancing. e.g. 1. He was busting some moves on the dancefloor - He was dancing well or demonstrating his dancing skilks 2. He was busting some moves on the basketball court - he was playing a good game of basketball or demonstrating his basketball skilks'.