Winter Nights (Old Norse: vetrnætr) was a specific time of year in medieval Scandinavia, held 28 days after the autumn equinox.
According to Zoega's Concise Dictionary of Old Icelandic, vetr-nætr referred to "the three days which begin the winter season".
The term is attested in the narrative of some of the Fornaldarsögur, mostly to express passage of time ("as autumn turned into winter").
[1] The exact term "winter nights" is not mentioned in the Ynglinga saga by Snorri Sturluson where (in chapter 8) the three great sacrifices of the year are prescribed:[2]
By contrast, álfablót was a sacrifice held at each homestead separately for the local spirits, under the explicit exclusion of any strangers.