As in parking level 1. Sketchy, poorly lit, parking area (i.e. the bottom level of a parking garage) where men go to perform promiscuous sexual acts on other men. The encounters must be completely anonymous in order to qualify under this definition.
"Yo JoeG, what are yo plans for today?"
"I have a meeting with the client, but then i'm gonna hit up P1 for some S&S"
"Joe, you is one Brokeback mothafucka"