P.O.S can stand for many things, such as Piece of Shit, Product of Society, Pissed off Stef, Promise of Skill, and Promise of Stress. He says it stands for whatever fits the song.
As of June 2010, he has three albums: Ipecac Neat, Audition, and Never Better
Jack: "That's P.O.S."
Mercedes: "Who's P.O.S?"
Jack: "A rapper coming from of the Great State of Minnesota."