Promcoming is a party held once a week in Lumpy Space. Finn and Jake are invited to one by Lumpy Space Princess in the episode "Trouble in Lumpy Space." It seems to be a popular event among Lumpy Space People, as quite a few of them attend. It is the place where Finn and Jake cure themselves of the lumps. It can be assumed Lumpy Space Princess and Melissa attend regularly, since Melissa reminded Lumpy Space Princess about it.
Trivia[]
"Promcoming" is a portmanteau of the words "prom" and "homecoming."