Christmas or Christmas Day is a holiday observed generally on December 25 to commemorate the birth of Jesus, the central figure of Christianity. The date is not known to be the actual birthday of Jesus, and may have initially been chosen to correspond with either the day exactly nine months after some early Christians believed Jesus had been conceived, the date of the winter solstice on the ancient Roman calendar, or one of various ancient winter festivals. Christmas is central to the Christmas and holiday season, and in Christianity marks the beginning of the larger season of Christmastide, which lasts twelve days.

Although nominally a Christian holiday, Christmas is also widely celebrated by many non-Christians, and many of its popular celebratory customs have pre-Christian or secular themes and origins. Popular modern customs of the holiday include gift-giving, music, an exchange of greeting cards, church celebrations, a special meal, and the display of various decorations; including Christmas trees, lights, garlands, mistletoe, nativity scenes, and holly. In addition, several similar mythological figures, known as Saint Nicholas, Father Christmas and Santa Claus among other names, are associated with bringing gifts to children during the Christmas season.

Because gift-giving and many other aspects of the Christmas festival involve heightened economic activity among both Christians and non-Christians, the holiday has become a significant event and a key sales period for retailers and businesses. The economic impact of Christmas is a factor that has grown steadily over the past few centuries in many regions of the world.