The section of the anus that cannot be seen without special night vision goggles that can see through the thick haze of feces. Excessive ass pounding can also open up the anus far enough to see the fourth eye.
Dawg 1: Dude I saw my Mom's fourth eye last night.
Dawg 2: Me too. I always beat off to your Mom through the bedroom window.
Dawg 2: Me too. I always beat off to your Mom through the bedroom window.
by GAPING BUTTHOLE MASTER March 11, 2012