The Sunday within the Octave of Christmas is a liturgical celebration in the Tridentine rite of the Roman Catholic Church

Roman Catholic Church

The Catholic Church, also known as the Roman Catholic Church, is the world's largest Christian church, with over a billion members. Led by the Pope, it defines its mission as spreading the gospel of Jesus Christ, administering the sacraments and exercising charity...

 which, in missals before 1962, takes place on either December 29, December 30, or December 31. If one of these three days is a Sunday, the celebration occurs on that day. If a Sunday should occur between December 25 and December 28 inclusive, the Mass of the Sunday within the Octave of Christmas is celebrated on December 30.

In the 1962 missal, the celebration is always on the Sunday within the octave, except that it moves to Friday, December 30, if Christmas itself is a Sunday.

In the Vatican II rite, this celebration was replaced with that of Holy Family

Holy Family

The Holy Family consists of the Child Jesus, the Virgin Mary, and Saint Joseph.The Feast of the Holy Family is a liturgical celebration in the Roman Catholic Church in honor of Jesus of Nazareth, his mother, the Blessed Virgin Mary, and his foster father, Saint Joseph, as a family...

, which the Tridentine calendar had assigned to the first Sunday after January 6.