Christmas or Christmas Day is an annual festival commemorating the birth of Jesus Christ, observed most commonly on December 25 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 ofAdvent or Nativity Fast and is prolonged by the Octave of Christmas and further by the season of Christmastide. Christmas Day is a public holiday in many of the world's nations, is celebrated culturally by a large number of non-Christian people,  and is an integral part of the Christmas and holiday season.