Someone who gets around, and often sleeps with members of a fraternity.
Person #1: Let's do some word association. Frat Mattress.
Person #2: Whitney
Person #1: Why?
Person #2: Because it just seems to fit.

or

Whitney is such a frat mattress.

by rusty bellige November 18, 2008
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1. Adjective. Loose person.
2. Female who sleeps with lots of men, usually members of a fraternity.
Laura is a big frat mattress.
by Matt December 7, 2004
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