(Note: Christ’s name is most commonly written in Greek, because the NT was originally written in Greek).
The labarum, an amalgamation of the two Greek letters rendered as ☧, is a symbol often used to represent Christ in Catholic, Protestant, and Orthodox Christian Churches.
However, the iconographic abbreviation of Xp or sometimes Xt is considered redundant since the X alone can be the linguistic equivalent of Christ.
Also, the common abbreviation for the word “cross” is a simple X. Thus the Kings Cross is often shortened to Kings X. This reinforces the assumption that Christ (who died on the cross) gets transformed into the common spelling of Xmas.
Wikipedia has this to say on the etymology of Christmas:
The word Christmas originated as a compound meaning “Christ’s Mass”. It is derived from the Middle English Christemasse and Old English Cristes mæsse, a phrase first recorded in 1038. “Cristes” is from Greek Christos and “mæsse” is from Latin missa. In Greek, the letter Χ (chi), is the first letter of Christ, and it, or the similar Roman letter X, has been used as an abbreviation for Christ since the mid-16th century. Hence, Xmas is often used as an abbreviation for Christmas.
Whichever one you decide to use is a matter of preference and not a so called attack on the Christian tradition celebrating Christmas (on December 25th). Although Christmas is celebrated on December 25th, thid date has less to do with Christianity than it does Mithraism. The Thinking Atheist reminds us:
December 25th was a date selected by the church, because no actual birth date for Jesus could be determined. It is the time of the Winter Solstice, and December 25th is also the traditional birthday of the Persian sun god, Mithra, whose birth legend includes shepherds, Magi, gifts, miracles, disciples and a virgin birth.
Clearly Xmas is not a “Christmas spirit” conspiracy to diminish the essence of Christ or otherwise ruin the holiday season. The simple fact of the matter is: Xmas is the literal equivalent of Christmas! It’s simply a different spelling. Lots of words have alternative spellings. Sceptic and Skeptic, for example.
†This moment of enlightenment has been brought to you from your friendly secular Atheist.†