1 definition by WTDAUSA

Top Definition
When the ass cheeks of a person no longer exist or for that matter curve inward creating a concave surface. Othewise known as a Cass= concave+ass. The opposite of convex.
She had such a flat ass that it had now turned into a Cass.

He had what you would call a Cass, the opposite of a bubble butt.
by WTDAUSA February 04, 2009

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