What is the X in X-mas?
a letter or announcement from the Pope to the Catholic world
so called because a lead bulla or seal was attached to the Pope's edict by a cord
in Roman Catholicism, an official papal letter or document. The name is derived from the lead seal (bulla) traditionally affixed to such documents. Since the 12th century it has designated a letter from the pope carrying a bulla that shows the heads of the apostles Peter and Paul on one side and the pope's signature on the other