Adj. The state of having your legs at a right angle to your body esp. while dancing. Often achieved by a female when dancing with a male at frat parties.
Man, Paul got that girl perpendicular last night.
Bro 1: Yo, so many girls went perpendicular on me last night.
Bro 2: Ohh, sounds like a good night.
Bro 1: Yeahh they were backing it up on me.