Tolkien called the joyful sudden turn at the end of a story a eucatastrophe.
He introduced the term in On Fairy-Stories, combining the Greek prefix eu-, meaning “good,” with catastrophe, meaning a decisive reversal or outcome. Tolkien used it for a sudden, favorable change that brings joy after danger, suffering, or apparent defeat.
For Tolkien, eucatastrophe was more than a convenient happy ending. He regarded it as a central feature of fairy stories and connected it with the possibility of hope. He also described the Resurrection of Christ as the greatest eucatastrophe in Christian history, reflecting his own Catholic beliefs.
Eucatastrophe is not identical to anagnorisis, which means a moment of recognition, or peripeteia, which means a reversal of circumstances. Those classical terms can overlap with events in a plot, but Tolkien’s word emphasizes the joyful outcome.