Christmas is a Christian traditional holiday celebrating the birth of Jesus Christ, though his true birthdate is unknown. It is celebrated every year on December 25th in most Western Christian churches (Protestant and Roman Catholic), and on the civil date of January 7 (1900 to 2099) in Eastern Orthodox churches which have not accepted either the Gregorian calendar or the Revised Julian Calendar reforms.
Many aspects of the Christian holiday, such as the Christmas Tree, the Yule Log, and the giving of presents, were taken from the earlier pagan holiday of Yule and the traditional celebrations of the Winter Solstice.
Originally, Christmas' date was set to correspond with Greco-Roman festivals. As early as A.D. 354, the Birth of Christ was celebrated on Dec. 25th in Rome. Other cities had other traditional dates.
In most Western countries, Christmas is also celebrated by the non-religious as a secular holiday and, often, an opportunity to catch up with one's extended family. It is also somewhat popular in Japan, encouraged by the commercial sector who see the opportunities in encouraging gift-giving.
Christmas is traditionally associated with the Northern Hemisphere winter, and thus winter motifs are prominent in Christmas decorations and in the Santa Claus myth. Residents of countries located in the tropics and the Southern Hemisphere thus experience somewhat of a dissonance between popular culture depictions of Christmas and their own balmy Christmas celebrations.
Christmas is, typically, the largest annual economic stimulus for the economies of celebrating Christian nations.