The word "Christmas" is sometimes abbreviated to "Xmas," a combination of the word "Christmas" and the ancient Greek letter that symbolized the word "Christ." The X has been used for hundreds of years in the Christian church as an initial for Jesus Christ.
Using the abbreviation "Xmas" is controversial among Christians. Some believe that it takes the "Christ" out of Christmas. Others argue that the X, still used as a symbol for Jesus in many Christian churches even today, is an acceptable abbreviation.
The X in "Xmas" is the Greek letter chi, which is the first letter of the name "Christ" in that language. Most Jews and followers of Jesus in the Holy Land 2,000 years ago communicated in Greek in their day-to-day lives, and the books of the New Testament were originally written in that language.
Christian historians aren't quite sure when the chi became the abbreviation for Christ. Some argue it was as early as the first century, but others aren't so sure. Either way, using the chi as an abbreviation had become an acceptable way of spelling "Christmas" by the 16th century. By then, the printing press had been invented, and abbreviating Christmas saved space, time and money.