Here's a comprehensive summary of the Wikipedia article on Christmas:

Christmas is an annual festival, primarily observed on December 25th, commemorating the birth of Jesus Christ and celebrated by billions worldwide as a significant religious and cultural holiday. The traditional narrative, known as the Nativity of Jesus, describes His birth in Bethlehem to Mary and Joseph in a stable, with angels proclaiming the news to shepherds. While Jesus's exact birth date is unknown, the church fixed December 25th in the early 4th century (a date that corresponds to January 7th for some Eastern Christian Churches using the Julian calendar).

The celebrations blend pre-Christian, Christian, and secular traditions, encompassing popular customs such as gift-giving, carols, elaborate decorations like Christmas trees and nativity scenes, and figures like Santa Claus associated with bringing gifts. Beyond its spiritual importance, Christmas has become a major global event, driving significant economic activity for businesses and retailers. The English word "Christmas" itself is derived from "Christ's Mass," first recorded as "Crīstesmæsse" in 1038.