Contrary to popular belief, pop-punk is not neccesarily shit like Good Charlotte. It is actually a more medolic punk. Think The Descendants, Bouncing Souls, Screeching Weasels, yes, even The Ramones.
Although, someone using the word is probabbly referring to shit bands like Good Charlotte, Newfoundglory and Brand New.
*Also not to be confused with the similiar yet SLIGHTLY less bad "skate-punk" (nofx, goldfinger, rancid)