why is christmas abbreviated to xmas

Oh, you know, it's just a way of shortening the word "Christmas" to make it easier to write and say. The "x" represents the Greek letter "chi", which is the first letter of "Christ" in the Greek alphabet. So "Xmas" is just a way of writing "Christ" without having to spell it out. It's a pretty common abbreviation for Christmas, and it's been used for centuries.