Twelve Days of Christmas

Short definition from Wiktionary

Noun

1. 1
   The season or time made up of the twelve days between Christmas and Epiphany; Christmas season, Christmas time, Christmastide, Twelvetide. The Christmas season traditionally ended with the feast of the Epiphany on January 6.
2. 2
   An 18th-century English Christmas carol which describes a series of successively grand gifts given on each of the twelve days of Christmas.