Christmas or Christmas Day (Old English: Crīstesmæsse, meaning "Christ's Mass") is an annual festival commemorating the birth of Jesus Christ,[6][7] observed generally on December 25[4][8][9] as a religious and cultural celebration among billions of people around the world.[2][10][11] A feast central to the Christian liturgical year, it closes the Advent season and initiates the twelve days of Christmastide, which ends after the twelfth night.[12] Christmas is a public holiday in many of the world's nations,[13][14][15] is celebrated culturally by a large number of non-Christian people,[1][16][17] and is an integral part of the Christmas and holiday season.