why is xmas short for christmas

Well, Xmas is actually a shortened form of the word "Christmas." It has been used for centuries as an alternative to the full spelling of the word. The letter "X" in Xmas is derived from the Greek letter "chi," which is the first letter of the word "Christ." So, Xmas is a way of abbreviating Christmas while still retaining its religious significance. It's a more efficient way to write the word, especially in situations where space is limited, such as in greeting cards or on Christmas decorations.