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.ch