Twelfth Night

Short definition from Wiktionary

Proper noun

1. 1
   A Christian festival marking the coming of Epiphany and concluding the Twelve Days of Christmas, traditionally falling on the evening of January 5 (i.e., on the eve of Twelfth Day, January 6), but also sometimes defined as falling on the evening of January 6 (i.e., on the evening of Twelfth Day itself).