The line formed where the underside of a woman's braless breast rests on the rib cage area of her torso, as seen from the side (usually due to sleeveless dresses or tops). Differs from side boob in that the breast must sag enough to produce the cleavage effect.
Dude, did you see Cameron Diaz's side cleavage at that awards show? So hawt!
de Rurouni KJS 16 Mai 2009