Christmas Eve, December 24, is the night before Christmas Day, which celebrates the birth of Jesus Christ.

The Christmas season liturgically begins on Christmas Eve, and is preceded by a four-week anticipatory and penitential period called Advent, which can include acts of almsgiving, fasting, and service while the season unfolds. The Mass of the Vigil is said in the late afternoon or early evening hours of December 24th. The Christmastide season continues through until the Feast of the Baptism of the Lord on the Sunday following the Solemnity of the Epiphany.

(... from Wikipedia on 2008-12-31 14:00:04 )