Fimbulvetr

In Norse mythology, Fimbulvetr (or fimbulvinter), commonly rendered in English as Fimbulwinter, is the immediate prelude to the events of Ragnarök. It means "great winter".

Summary
Fimbulvetr is the harsh winter that precedes the end of the world and puts an end to all life on Earth. Fimbulwinter is three successive winters, when snow comes in from all directions, without any intervening summer. Then, there will be innumerable wars.

The event is described primarily in the Poetic Edda. In the poem Vafþrúðnismál, Óðinn poses the question to Vafþrúðnir as to who of mankind will survive the Fimbulwinter. Vafþrúðnir responds that Líf and Lífþrasir will survive and that they will live in the forest of Hoddmímis holt.

The mythology might be related to the extreme weather events of 535–536, which resulted in a notable drop in temperature across northern Europe. There have also been several popular ideas about whether or not the particular piece of mythology has a connection to the climate change that occurred in the Nordic countries at the end of the Nordic Bronze Age from about 650 BC. Before that climate change, the Nordic countries were considerably warmer.

In Denmark, Norway, Sweden and other Nordic countries, the term fimbulvinter is still used to refer to an unusually cold and harsh winter.

Etymology
Fimbulvetr comes from Old Norse, meaning "awful, great winter". The prefix "fimbul" means "the great/big" so the correct interpretation of the word is "the great winter".