An LNDP is a Late-Night Dance Party. These are frequented by drunk college students, very late, after they have already left other parties and consumed their fill of alcohol. The LNDP is often college-sponsored so there is no alcohol, but people have pre-gamed anyway. Also there is always a lame DJ.
Todd: Dude, after the kegger at Theta House tonight, there's an LNDP at the Social Hall.
Mike: Awesome. There's gonna be so many wasted freshman chicks for me to spit game on. I will DP all night at this thing... and then hopefully you and me can bring one back and pull another kind of DP in our dorm room afterwards!