The Hundred-Year Winter is a time period in the fictional Narnia universe created by C.S. Lewis. It takes place from 900–1000 Narnia time. The White Witch Jadis cast a spell to make it Winter all year round, but never reaches Christmas. But throughout the story, Aslan is entering Narnia and his presence weakens The White Witch, Jadis, causing Spring and Father Christmas to slowly appear. Aslan also brings Peter, Lucy, Susan, and Edmund to Narnia to fulfill the Prophecy of The Four Thrones ("When two daughters of Eve and two sons of Adam sit together in throne at the Cair Paravel, the reign of the White Witch will be over and done.) This would put an end to White Witch's plan and her reign and the endless winter would come to an end. (The final days of the Hundred Year Winter occur during The Lion, the Witch, and the Wardrobe.)
The Hundred-Year Winter bears strong parallels with the Norse Fimbulwinter.