Christmas or Christmas Day is a holiday generally observed on December 25 (with alternative days of January 6, 7 and 19) to commemorate the birth of Jesus, the central figure of Christianity. The exact birthday of Jesus is not known, and historians place his year of birth some time between 7 BC and 2 BC. Narratives of his birth are included in two of the Canonical gospels in the New Testament of the Bible. The date of Christmas may have initially been chosen to correspond with either the day exactly nine months after Christians believe Jesus to have been conceived, the date of the Roman winter solstice, 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 celebrated by an increasing number of non-Christians worldwide, 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 Christmas 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 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.