The area that blocks the vagina from men. Even though most men would NEVER in there lives be caught dead trying to enter this area nor want to be around it.
Also a nickname for a girl that you do not want around nor within 500 feet of you.
Guy #1: dude... Duh flap is somewhere... i can smell cheese.
Guy #2: dude just stay still... she can't see if you, if you don't move.