frat matress Share definition Flag A college girl, or townie who spends most of her time under 1 or more frat boys. My roomate is such a frat matress, if i put her under a blacklight the girl would glow. frat matress by Lylli December 14, 2006 0 0 Get merch Get the frat matress mug. Buy Now — $32.95 See more merch