From the Urban dictionary:
Quad-boob occurs when a woman's bra is snug enough that part of the breasts squeeze up above the fabric of the cups, creating an upwelling of boobs visible even with a shirt on top. To the unlearned boob admirer it may give the impression of four boobies.
"Check out that quad-boob over there, she must have escaped from Jabba's Palace."
OK, yes. I had to look it up. I'm sure I'm not the only one.
Hehehehhe that might be the best definition for it ever