A term used to express how hot a girl is. Two piece is a girl that is so hot that you'd want to rip her into 2 pieces. This term can be used up to 8 pieces max but even a 4 piece is really rare so don't jump into calling a girl 4 piece so fast.
Joey: Dude check out that 2 piece!
Joey: Over there
Chandler: Damn! she could even be a 4 piece.