The 12-day period beginning with Christmas and ending with the Feast of the Epiphany is called the Twelve Days of Christmas.
In the traditional Christian calendar, the period begins on December 25 and ends on January 5, with Epiphany observed on January 6. New Year's Day falls within this Christmas season, although exact customs and counting practices can vary among Christian traditions.
The period gave its name to the well-known English Christmas carol “The Twelve Days of Christmas.” In the song, successive verses describe gifts associated with each day, but the carol is not a calendar guide to New Year's Eve customs.
A common mix-up is placing the twelve days before Christmas. That earlier period is Advent, which prepares for Christmas. The Twelve Days instead begin on Christmas Day and continue through the first days of January.