An approximate 18" in diameter plastic, round container that is filled with crappy to mediocre (at best) quality beer. The recepticle is tapped, then is typically hovered over by a group of broke, underage college students who proceed to drink the equivalent of 8 beers out of their first 12 pack (or so they say). Traditionally, this festivity occurs around ones payday or b-day (when they receive money from their grandparents).
Hey everyone, I got paid today. Let's get a party ball in the dorm room and we'll be really cool. We'll have enough to keep drinking off of it for 3 weeks, when it's nice and rancid.