The person(s) on the set of an adult film whose sole purpose is to clean up any stray male ejaculate (i.e. jizz) that happens to have hit the floor or furniture
1. Taken from the classic movie, Clerks, a gizz mopper is an employee of janitorial status who works at a nudie booth. When satisfied customers blow their loads on the glass... this really doesn't require much more explanation.