When you go to a metal gig, or any show with a pit and are involved in it.
You then come home and wake up the next morning in agony from all the kicks and bodies that came flying out at you the night before.
Similar to a hangover, but physically more painful.
Guy1 : "Mate, how good was the black dahlia gig last night?"
Guy2: "Yeah it was immense, but i woke up with a terrible moshover."