The Moomins are the central characters in a series of books by Finnish writer Tove Jansson, originally published in Swedish. They are a family of Scandinavian trolls who are white, round and furry in appearance, with large snouts that make them resemble hippopotamuses. The carefree and adventurous family live in their house in Moominvalley, though in the past their residences have included a lighthouse and a theatre.
moomintroll is a troll that lives with his family in moominvalley, he's got alot of friends (snorkmaiden, snufkin, little my etc.) but every winter his boyfriend snufkin goes away and that makes moomintroll super depressed.
Moomin has several uses. It can be used in the same way as, "vibing", and can even be used to show that you are looking forward to something. Similar to "Mmmmm, sandwich time soon".
EXAMPLE 1
Person 1: Hey, what are you up to?
Person 2: Ahh, ya know, just moomin