The Mass will be that of the feast of the Dedication of the Lateran Basilica in Rome.
The Basilica of St. John Lateran is the cathedral of Rome. This is not St. Peter's, but it is the Pope's cathedral. Also called the Church of Holy Saviour or the Church of St. John Baptist, it was the baptism church of ancient Rome. It was built in the time of Constantine and was consecrated by Pope Sylvester in 324. This feast became a universal celebration in honor of the basilica called "the mother and mistress of all churches of Rome and the world" (omnium urbis et orbis ecclesiarum mater et caput) as a sign of love for and union with the See of Peter.