It is an acronym for Product of Poor Parenting.
It can be used to describe children who are loud, rude, inapropriate, stinky, horny, and unmotivated.
A child can be characterized as any one of those, but it is not his/her fault, it is the fault of the parents. The child is intrinsicly well off, regardless of how much the parents screwed 'em up.
Camp Director: No, no, no. Johnny is a POPP. It's his parents fault that he behaves so poorly.