Christmas or Christmas Day is an annual festival commemorating the birth of Jesus Christ, observed most commonly on December as a religious and cultural celebration among billions of people around the world.A feast central to the Christian liturgical year, it is prepared for by the season of Advent or the Nativity Fast and initiates the season of Christmastide,which historically in the West lasts twelve days and culminates on Twelfth Night in some traditions, Christmastide includes an Octave.Christmas Day is a public holiday in many of the world's nations is celebrated culturally by a large number of non-Christian people.most Christians celebrate Christmas on the date of December 25 in the Gregorian calendar, which is also the calendar in near-universal use in the secular world.