Xmas is a synonym for Christmas. It should be capitalized as well. Xmas may be pronounced as /ˈɛksməs/ or /ˈkrɪsməs/. It does not require a hyphen.
A common myth is that Xmas originated from someone wanting to take Christ out of Christmas. However, Xmas actually goes all the way back to the fifteenth century. The letter x begins the Greek word for Christ and so it was used as a shorthand for those who knew the Greek alphabet. Christians were Xtians and Christmas was Xmas.
Sometimes you may see the term spelled Xtmas or Xpmas, though the latter is usually only found in articles discussing the history of the term. This spelling variation comes from the second letter of the Greek word for Christ, which is ρ (Rho). This is transliterated to English as a p or sometimes as a t, presumably by those who did not know the Greek letters semblance to p and substituted it for the last letter in Christ’s name.
Even though there is no basis for the myth that Xmas takes Christ out of Christmas, most readers will not know this. If you are concerned about offending your audience, it is best to spell out the name of the holiday.
Once again the quality of donations to our Kiddies Xmas Fund is more impressive than the quantity — again only four donations but well over 10,000 pesos (thanks largely to the Chain Gang, who invariably triumph over their rivals the Gourmandizers by chipping in throughout the year while the G-men rely on spontaneous Yuletide generosity in the closing weeks). [Buenos Aires Herald]
Payday 2 recieved a nice update on Steam to compliment the ‘White Xtmas’ annual heist that’s going on, but the update didn’t come alone. [Game Zone]