A term used to describe the phenomena that occurs when one's zipper is down, thus revealing one's penis.
Oh my god, do you realize that you were gapping in front of the entire audience? You almost gave an elderly woman a black eye with that mushroom sprout of yours!
Person 1: Hey dude, have you seen Arnold Schwarzenegger's tooth gap?
Person 2: Oh man, I'd gap that shit any day!
Person 1: Yeah, he could get a good gapping.