What is a type of public decree or charter issued by a pope of the Catholic Church called?
A papal bull is a type of public decree, letters patent, or charter issued by a pope of the Catholic Church. It is named after the leaden seal (bulla) that was traditionally appended to the end in order to authenticate it.
Papal bulls have been in use at least since the 6th century, but the phrase was not used until around the end of the 13th century, and then only internally for unofficial administrative purposes. However, it had become official by the 15th century, when one of the offices of the Apostolic Chancery was named the "register of bulls".
By the accession of Pope Leo IX in 1048, a clear distinction developed between two classes of bulls of greater and less solemnity. The majority of the "great bulls" now in existence are in the nature of confirmations of property or charters of protection accorded to monasteries and religious institutions.
Since the 12th century, papal bulls have carried a leaden seal with the heads of the Apostles Saint Peter and Saint Paul on one side and the pope’s name on the other. Papal bulls were originally issued by the pope for many kinds of communication of a public nature, but by the 13th century, papal bulls were only used for the most formal or solemn of occasions.
Modern scholars have retroactively used the word "bull" to describe any elaborate papal document issued in the form of a decree or privilege, solemn or simple, and to some less elaborate ones issued in the form of a letter.