The Meaning of the Word Christmas

Rather than try and write a definition, here's a good one I found online:

https://www.celebratingholidays.com/?page_id=996

By the Middle Ages, Christians were celebrating the remarkable event of Jesus’ birth with an extended season that began with Advent (four Sundays before Christmas) and continued for the 12 Days after Christmas (up until Epiphany on January 6th). The time preceding Christmas used to be a solemn time of fasting, whereas the days after Christmas were the time of celebration. Christians looked forward to the Midnight Mass of Christmas Eve with great anticipation, because it was the service that marked the transition from fasting to feasting. This service, known as “Christ’s Mass,” eventually became a description for celebrations of Jesus’ birth throughout the world. The word Christmas has its origin from the old English term Cristes Maesse, meaning “Christ’s Mass.”