Christmas, also referred to as Christmas Day, is an annual holiday celebrated on December 25 that commemorates the birth of Jesus of Nazareth. The day marks the beginning of the larger season of Christmastide, which lasts twelve days. The nativity of Jesus, which is the basis for the anno Domini system of dating, is thought to have occurred between 7 and 2 BC. December 25 is not known to be Jesus' actual date of birth, and the date may have been chosen to correspond with either a Roman festival or the winter solstice.

Modern customs of the holiday include gift-giving, Church celebrations, and the display of various decorations—including the Christmas tree, lights, mistletoe, nativity scenes, and holly. Santa Claus (also referred to as Father Christmas, although the two figures have different origins) is a popular mythological figure often associated with bringing gifts at Christmas for children. Santa is generally believed to be the result of a syncretization between Saint Nicholas and elements from pagan Nordic and Christian mythology, and his modern appearance is believed to have originated in 19th century media.

Christmas is celebrated throughout the Christian population, but is also celebrated by many non-Christians as a secular, cultural festival. Because gift-giving and several other aspects of the holiday involve heightened economic activity among both Christians and non-Christians, Christmas has become a major event for many retailers.