(noun) When a group of friends decide to either go out/stay in to get drunk then proceed to laying on their floor with blankets and pillows staying up into the odd hours of the night. Such activities include general gossip, television/movie viewing, and other forms of entertainment. It is essentially a sleep over for adults who are drunk enough to enjoy each others company for an extended period of time.
Linda: "What are you doing tonight?"
Karen: "Not sure, we might have a slumpover. Theres still a bunch of 40s left over from the weekend in the fridge and Jill just got Netflix. Wanna come?"
Linda: "Damn that sounds fun but I have exams tomorrow."
Karen: "Ah, well maybe next time."