n. A social gathering that occurs after a party, especially after a rave.
2002
At early-morning "after-parties," friends would recover from the hard beats of electronica (and the disorienting effects of Ecstasy) with the quiet balm of ambient music.
1980 (earliest)
"It was funny," said a jovial and very relaxed Walter Cronkite, "but I can't remember a damn thing." He said this about 1:45 a.m., deeply immersed in the evening's biggest afterparty, held by The Los Angeles Times and The Detroit News.