A combination of two words, namely "what's" and "that".

A lazy, slang way to ask the question "What's that?"
Boy 1: "Hey did you hear about Daz and Sarah gettin' nakie in the club last week?"

Boy 2: "Wassat?"

Anatomist: "So I was studying the Hyopglossal nerve today and discovered it wasn't as close to the ansa cervicalis as I had previously thought."

Uneducated person: "Wassat?"

Pervert: "I bought a whiz bang sex machine with double pop rivets today."

Naive person: "Wassat?"
by catastridphe July 17, 2006
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