The Twelve Days of Christmas

The Twelve Days of Christmas, also known as Twelvetide, is a festive Christian season celebrating the Nativity of Jesus. 

In some Western ecclesiastical traditions, "Christmas Day" is considered the "First Day of Christmas" and the Twelve Days are 25 December to 5 January, inclusive, with 6 January being a "thirteenth day" in some traditions and languages. 

However, 6 January is most often considered Twelfth Day/Twelfth Night with the Twelve Days "of" Christmas actually after Christmas Day from 26 December to 6 January. 

For many Christian denominations—for example, the Anglican Communion and Lutheran Church—the Twelve Days are identical to Christmastide, but for others, e.g., the Roman Catholic Church, Christmastide lasts longer than the Twelve Days of Christmas.