A towel, rug or other material laid out to catch sex fluids and juices during coitus to avoid dampening or soiling the underlying surface.
We put down a towel for our cum mat so we didn’t get jizz all over my mom’s new bed spread.
My boyfriend put a tea towel down on the kitchen counter for a cum mat and proceeded to bang my ass.
Our cum mat was soaking wet after I squirted multiple times but the mattress was nice and dry.