Traditionally, people thought of Christmas as having 12 days — not including Christmas.
Christmas Day itself was reserved as a holy day of religious observances. The 12 days of Christmas began on what is now Boxing Day, the day after Christmas. They were a time of relaxed work for all, feasting, merriment and celebration.
Six of the days fall in the year that is ending; the other six fall in the year that is coming.
The final day, January the 6th, was called Epiphany. This is when the Wise Men reputedly found and visited Jesus. It marks the end of all Christmas celebrations, and was a time when people would take down Christmas decorations and pack them away for another year.