Christmas is an annual holiday that celebrates the birth of Jesus. It refers both to the day celebrating the birth; as well as to the season which that day inaugerates, and which concludes with the Feast of the Epiphany. The date of the celebration is traditional, and is not considered to be his actual date of birth. Christmas festivities often combine the commemoration of Jesus' birth with various cultural customs, many of which have been influenced by earlier winter festivals.
In most places around the world, Christmas Day is celebrated on December 25. Christmas Eve is the preceding day, December 24. In the United Kingdom and many countries of the Commonwealth, Boxing Day is the following day, December 26. In Catholic countries, Saint Stephen's Day or the Feast of St. Stephen is December 26. The Armenian Apostolic Church observes Christmas on January 6. Eastern Orthodox Churches that still use the Julian Calendar celebrate Christmas on the Julian version of 25 December, which is January 7 on the more widely used Gregorian calendar, because the two calendars are now 13 days apart.
The word Christmas originated as a contraction of "Christ's mass". It is derived from the Middle English Christemasse and Old English Cristes mæsse, a phrase first recorded in 1038, compounded from Old English derivatives of the Greek christos and the Latin missa. In early Greek versions of the New Testament, the letter ? (chi), is the first letter of Christ. Since the mid-16th century ?, or the similar Roman letter X, was used as an abbreviation for Christ. Hence, Xmas is often used as an abbreviation for Christmas.
After the conversion of Anglo-Saxon Britain in the very early 7th century, Christmas was referred to as geol, the name of the pre-Christian solstice festival from which the current English word 'Yule' is derived.
The prominence of Christmas Day increased gradually after Charlemagne was crowned on Christmas Day in 800. Around the 12th century, the remnants of the former Saturnalian traditions of the Romans were transferred to the Twelve Days of Christmas (26 December - 6 January). Christmas during the Middle Ages was a public festival, incorporating ivy, holly, and other evergreens, as well as gift-giving.
Modern traditions have come to include the display of Nativity scenes, Holly and Christmas trees, the exchange of gifts and cards, and the arrival of Father Christmas or Santa Claus on Christmas Eve or Christmas morning. Popular Christmas themes include the promotion of goodwill and peace.
Information Source: http://en.wikipedia.org/wiki/Christmas