There is a common misconception that the word Xmas is an attempt to secularize the Christmas tradition by removing the word “Christ”. On the contrary, the word was used by religious people as far back as the 16th century, mostly as a convenient abbreviation.
The “X” comes from the Greek letter Chi, which is the first letter of the Greek word “Χριστός”, which in English translates into “Christ”. (Meanwhile, the “-mas” part is from the Latin-derived Old English word for Mass).
Granted, some Christians regardless dislike the use of “xmas” in place of Christmas, while by the same token many irreligious people prefer the former as a more secular version of the latter.