The term “Christmas season” is considered synonymous with Christmastide,a term associated with Yuletide, which runs from December 25 (Christmas Day) to January 5 (Epiphany Eve), popularly known as the 12 Days of Christmas.
That mean Christmas is not just one day.
In the Christian tradition the Christmas season is a period beginning on Christmas Day (December 25). In some churches the season continues until the day before the Epiphany, which is celebrated either on January 6 or on the Sunday between January 2 and 8. In other churches it continues until the feast of the Baptism of the Lord, which falls on the Sunday following the Epiphany, or on the Monday following the Epiphany if the Epiphany is moved to January 7 or 8. If the Epiphany is kept on January 6, the Church of England’s use of the term Christmas season corresponds to the Twelve Days of Christmas, and ends on Twelfth Night.
This short Christmas season is preceded by Advent, which begins on the fourth Sunday before Christmas Day: the majority of the secularized Christmas and holiday season falls during Advent. The Anglican Communion and some Protestant churches follow the Christmas season with an Epiphany season which lasts until Shrove Tuesday which is also known as Mardi Gras or ‘Fat Tuesday’. Other European cultures have their own carnival festivities between new year and Lent.