Christmas is the festival that celebrates the birth of Jesus, the founder of one of the world's most important religions, Christianity. Christmas means, literally, 'Christ's Mass', the Mass--known to some Christians as Communion--being the single most important aspect of a Christian worship service.
The followers of Jesus believed that Jesus was the Christ, or Messiah, whose coming was prophesied in the Jewish Tanakh (which Christians call the Old Testament). They therefore became known as 'Christians'. Christians believe, too, that Jesus was divine, and is the Son of God.
Christmas, the celebration of Jesus' birth, is perhaps the most popular celebration of Christianity. In most parts of the world, Christmas is celebrated on December 25. The Armenian Apostolic Church celebrates Christmas on January 6, while some Eastern Orthodox Churches follow the old Gregorian calendar and celebrate it on January 7, the date which corresponds to December 25 on the Julian calendar (the calendar that most of the world now follows).
Scholars are not certain of the correct date of Jesus' birth. Ancient cultures used to celebrate the winter solstice, which falls usually on December 21 or 22 in the northern hemisphere. The winter solstice marks the longest night of the year - after this, the nights start becoming shorter and the days longer. Ancient cultures celebrated this time of year with feasting and merry-making. In Roman times, one of the most important winter festivals was the Saturnalia, a festival to honour the Roman god Saturn.This festival usually began on December 17 and continued till December 24. The early Christian Church instituted December 25 as the day for the celebration of Jesus' birth, probably in an attempt to convert people to Christianity, in a way that would not force them to give up their celebrations entirely, and so make them more willing to adopt the new religion.