The origin of Christmas is the birth of Jesus, so the word Christmas contains the name of Jesus Christ. Christmas has gradually evolved from a religious holiday to a public holiday celebrated by non believers in Western countries.
But some non believers invented the word Xmas to distinguish themselves from Catholics such as Christ during this holiday, turning Christ into an unknown number X in mathematical equations. Xmas is pronounced according to the pronunciation of Christmas, but its meaning is to indicate that one is not a Christian.
In fact, Xmas (also known as X-mas) means Christmas. Xmas is an abbreviation that is not commonly believed. The substitution of X for Christ in Christmas is due to the Greek word for Christ Χριστο The capitalization of the first letter of s is very similar to the English X, and early Christians often used X as the abbreviation for Christ because the language was Greek. After the language developed into English, some people simply wrote Christmas as Xmas. Xmas is a mixture of Greek and English, rather than a formal English word. Many foreign merchants hang up posters with the words' Merry Xmas' during Christmas, but still use Christmas as the correct Christmas name in formal occasions.
In modern society, the pursuit of simplicity is increasing, and more and more people are using Xmas instead of Christmas. However, in formal occasions, it is still more appropriate to use formal Christmas.