In Norse mythology’s Ragnarok, Fimbulwinter lasts three successive winters with no summer between them.
The winter is described as an extreme climatic disaster that comes before the final conflict. Snow, bitter cold, and harsh conditions spread across the world, helping destroy social order and prepare the way for Ragnarok.
The name Fimbulwinter comes from Old Norse and is commonly translated as “Great Winter” or “Mighty Winter.” It is especially associated with the account in the Poetic Edda poem Vafþrúðnismál and with later descriptions in the Prose Edda.
Fimbulwinter is sometimes confused with Ragnarok itself. It is not the apocalypse but one of its major precursors. The three winters are also distinct from the broader darkness and disasters that occur during the final battle.