Sunday within the Octave of Christmas
The Sunday within the Octave of Christmas is a liturgical celebration in the Tridentine rite of the Roman Catholic Church 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, which falls within the Christmas season.
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, which the Tridentine Calendar had assigned to the first Sunday after January 6.