Cum that was expelled through masturbation, ie- "Jacking", and has not been cleaned up, allowing it to go shiny and slightly crisp, like cake frosting.
Typically found in teenagers bedrooms, although fully grown men that have wank addictions have been known to jack frost their carpet on a regular basis.
Danielle thought she had hit the jackpot with Steven. He was kind, considerate, and seemed to be very house proud. She relaxed happily on the sofa, thinking about how great her relationship was- until she noticed the Jack Frosting on one of the cushions.