CHRISTMAS (in old English, Cristes maesse) is a festival celebrated on Dec. 25, that commemorates the Incarnation of the Word of God in the birth of Jesus Christ. In the Book of Common Prayer (BCP) it is also called The Nativity of Our Lord Jesus Christ. It is the season when we proclaim the unique nature of our God – that He does not stand aloof from us, but fully enters our lives.
In the Book of Common Prayer (BCP) the season of Christmas lasts for 12 days, beginning on the 25th and ending on the 12th night, or January 5th of the next year (the day before the EPIPHANY). The season includes Christmas Day, the First Sunday after Christmas Day, the Holy Name of Our Lord Jesus Christ, and may include the Second Sunday after Christmas Day. The color used in Christmas liturgies is white, symbolizing purity, joy, and hope.
The first liturgy of Christmas is the Eve of (prior to) that day. The late night liturgy, called the Christ Mass is high-light of our year. Other liturgies are offered earlier that afternoon and on Christmas morning. In many parishes, the main liturgical celebrations of Christmas take place on Christmas Eve. A variety of resources can be used during Christmas, including a Station at a Christmas Crèche, a Christmas Festival of Lessons and Music, and seasonal blessings during the Christmas season.
Source: https://episcopalchurch.org/calendar-church-year; https://episcopalchurch.org/library/glossary/christmas-or-christs-mass