Christmas or Christmas Day (Old English: Crīstesmæsse, meaning "Christ's Mass") 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 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, and is an integral part of the holiday season, while some Christian groups reject the celebration. In several countries, celebrating Christmas Eve on December 24 has the main focus rather than December 25, with gift-giving and sharing a traditional meal with the family.
Although the month and date of Jesus' birth are unknown, by the early-to-mid 4th century the Western Christian Church had placed Christmas on December 25, a date which 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 churches celebrate Christmas on the 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. In the Council of Tours of 567, the Church "declared the twelve days between Christmas and Epiphany to be one unified festal cycle", thus giving significance to both December 25 and January 6.
Although it is not known why December 25 became a date of celebration, there are several factors that may have influenced the choice. December 25 was the date the Romans marked as the winter solstice, and Jesus was identified with the Sun based on an Old Testament verse. The date is exactly nine months following Annunciation, when the conception of Jesus is celebrated. Finally, the Romans had a series of pagan festivals near the end of the year, so Christmas may have been scheduled at this time to appropriate, or compete with, one or more of these festivals.
The celebratory customs associated in various countries with Christmas have a mix of pre-Christian, Christian, and secularthemes and origins. Popular modern customs of the holiday include gift giving, completing an Advent calendar or Advent wreath, Christmas music and caroling, lighting a Christingle, an exchange of Christmas cards, church services, a special meal, and the display of various Christmas decorations, including Christmas trees, Christmas lights, nativity scenes, garlands, wreaths, mistletoe, and holly. In addition, several closely related and often interchangeable figures, known as Santa Claus, Father Christmas, Saint Nicholas, and Christkind, are associated with bringing gifts to children during the Christmas season and have their own body of traditions and lore. Because gift-giving and many other aspects of the Christmas festival involve heightened economic activity, the holiday has become a significant event and a key sales period for retailers and businesses. The economic impact of Christmas has grown steadily over the past few centuries in many regions of the world.