From old English Cristes maesse (Christ's Mass), older still, Yule, from the Germanic root geol. In some languages:
The traditional Christmas is not a single day but a prolonged period, normally from 24th December to 6th January. This included the New Year, thus increasing the festival value of Christmas.
From old Persian language, a priest of Zarathustra (Zoroaster). The Bible gives us the direction, East and the legend states that the wise men were from Persia (Iran) - Balthasar, Melchior, Caspar - thus being priests of Zarathustra religion, the mages. Obviously the pilgrimage had some religious significance for these men, otherwise they would not have taken the trouble and risk of travelling so far. But what was it? An astrological phenomenon, the Star? This is just about all we know about it.
The practice of sending Christmas greeting cards to friends was initiated by Sir Henry Cole in England. The year was 1843 and the first card was designed by J.C.Horsley. It was commercial - 1000 copies were sold in London. An English artist, William Egley, produced a popular card in 1849. From the beginning the themes have been as varied as the Christmas customs worldwide.
The astrological/astronomical phenomenon which triggered the travel of the Magi to give presents to child Jesus. Variously described as a supernova or a conjunction of planets it supposedly happened around the year 7 BC - the most probable true birth year of Christ. Star is often put to the top of the Christmas tree.
The traditional date for the appearance of Santa Claus, obviously from the birthdate of Jesus (the word Christmas is from old English, meaning Christ's mass). This date is near the shortest day of the year, from old times an important agricultural and solar feasting period in Europe. The actual birthday of Jesus is not known and thus the early Church Fathers in the 4th century fixed the day as was most convenient. The best fit seemed to be around the old Roman Saturnalia festival (17 - 21 December), a traditional pagan festivity with tumultuous and unruly celebrations. Moreover,in 273 Emperor Aurelianus had invented a new pagan religion, the cult of Sol Invictus (invincible sun, the same as the Iranian god Mithra), the birthday of this god being 25th December (natalis sol invicti). The Christian priests obviously saw this choice as doubly meritorious: using the old customary and popular feasting date but changing the rough pagan ways into a more civilized commemoration.
The first mention of the birthday of Jesus is from the year 354. Gradually all Christian churches, except Armenians (celebrating 6th January which date is for others the baptismal day of Jesus and the day of the three Magi), accepted the day. In American/English tradition the Christmas Day itself is the day for Santa, in German/Scandinavian tradition the Christmas Eve is reserved for presents.
Jesus was born in a stable in Bethlehem. In Catholic countries this fact is brought to mind with miniature replicas of the nativity scene. The manger, animals, miniatures of Jesus, Joseph, Maria, the shepherds and the Three Magi are part of this very popular symbol. It was started (says the legend) by St Franciscus of Assisi. The Pope has his own in Rome but nowadays the custom is followed in Protestant countries, too.
Sacred to ancient druids and a symbol of eternal life the same way as Christmas tree. The Romans valued it as a symbol of peace and this lead eventually its acceptance among Christmas props. Kissing under mistletoe was a Roman custom, too.
Anything goes nowadays. In old times they were simple, wood, paper, straw and often very intricate. Themes follow the general taste of each time but national traditions can be discerned even now.
There are many roots of this custom. There is St.Nicholas the anonymous benefactor, there is the tradition of Magi giving precious gifts to Jesus, there is the Roman custom of giving gifts of good luck to children during Saturnalia. The day of gift giving varies greatly in different Christian cultures and times:
The giver of the presents are many: Jesus himself, Old Father Christmas, Santa Claus, a Goat, Befana (the female Santa in Italy), the three Magi, Christmas gnomes, various Saints, the Kolyada (in Russia), the Joulupukki (in Finland). The oldest Finnish tradition did not necessarily involve a giver of the presents at all: an unseen person threw the gifts in from the door and quickly disappeared.
The Catholic Church valued music greatly and it is no wonder that the early Christmas songs date from 4th century (the earliest known is Jesus refulsit omnium by St.Hilary of Poitiers). The Mediaeval Christmas music followed the Gregorian tradition. In Renaissance Italy there emerged a lighter and more joyous kind of Christmas songs, more like the true carols (from the French word caroler, meaning to dance in a ring). These songs continued to be religious and in Latin, though. In Protestant countries the tradition, as everything Christmas-related, intensified.
Luther wrote and composed his song "From Heaven above I come to You". Music by Handel and Mendelssohn was adapted and used as Christmas carols. The old Finnish/Swedish collection Piae Cantiones was translated and published in English in mid - 19th century. The most famous of all, Silent Night (Stille Nacht, heilige Nacht) was written by the Austrian parish priest Joseph Mohr and composed by Franz Gruber, church organist, in 1818. In 19th century and later many popular songs were written by composers (e.g. Adam, Sibelius). The themes of songs surpassed religion and the totality of Christmas paraphernalia found its way to carol music.
Religious plays were part of the Medieval Christian tradition and many of them were connected with Christmas. The plays were often communal with pageants and general participation. A popular theme was the coming of the Magi (the Three Kings), because the plot allowed lots of pomp and decorative props to please the audience. These plays live on in many places, for instance in Finland in the form of the traditional Star Boys drama.
Christmas means eating in most parts of the Christian world. In old societies hunger was the supreme king and eating was the highest contrast, the supreme way to nirvana. Meat of some kind was the most important dish (was this connected with the words of Jesus, "this is my flesh"?), often pork, ham,goose, (later turkey), fish (carp, salmon). An innumerable variety of cakes and pastries, often very intricate and only baked for Christmas were and are known throughout the world. Cakes could be hung from the Christmas tree, too.