Christmas 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 preceded 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 religiously by a majority of Christians, as well as culturally by many non-Christians, and forms an integral part of the holiday season. In several countries, celebrating Christmas Eve has the main focus rather than Christmas Day.

Although the month and date of Jesus’ birth are unknown, by the early-to-mid fourth century the Western Christian Church had placed Christmas on December 25, a date that was later adopted in the East. Today, most Christians celebrate on December 25 in the Gregorian calendar, which has been adopted almost universally in the civil calendars used in countries throughout the world. However, some Eastern Christian Churches celebrate Christmas on December 25 of the older Julian calendar, which currently corresponds to January 7 in the Gregorian calendar, the day after the Western Christian Church celebrates the Epiphany. This is not a disagreement over the date of Christmas as such, but rather a preference of which calendar should be used to determine the day that is December 25.