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The name given for the motion natural breasts make during a woman's movement, usually while involved in a sexual act; originating from the term "Waterbed Motion"

The rhythmic movements of a woman's body will be mimiced by the movement of her chest in a way that is almost as hypnotic as a lavalamp. Women that have undergone implant surgery to make their breasts unnecessarily large (boob job) will usually lose The Wabum Effect

Without naming it specifically, Robin Williams helped to define the Wabum Effect by saying "Fake tits are like nazis; they don't laugh, they don't dance, it's just HU-YEAH! I'M WALKING HERE!"
Man 1: Look at the rack on her!
Man 2: Nah, not my style. They're totally fake, I like a girls tits to wabum, it's just sexier when they move like that!
Man 1: I don't care if they wabum or not!
Man 2: Then go for it!
by Troy LeVassuer June 19, 2006
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