Papal Bull
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) traditionally appended to authenticate it.
In terms of content, the bull is simply the format in which a decree of the pope appears. Any subject may be treated in a bull, and many were and are, including statutory decrees, episcopal appointments, dispensations, excommunications, apostolic constitutions, canonizations, and convocations.
The bull was the exclusive letter format from the Vatican until the 14th century, when the papal brief appeared. The brief is the less formal form of papal communication and was authenticated with a wax impression, now a red ink impression, of the Ring of the Fisherman. There has never been an exact distinction of usage between a bull and a brief, but nowadays most letters, including encyclicals, are issued as briefs.
A bull's format formerly began with one line in tall, elongated letters containing three elements: the pope's name, the papal title "Episcopus Servus Servorum Dei" ("Bishop, Servant of the Servants of God"), and its incipit, i.e., the first few Latin words from which the bull took its title for record-keeping purposes, but which might not be directly indicative of the bull's purpose.
The body of the text was often very simple in layout, and it had no specific conventions for its formatting. The closing section consisted of a short "datum" that mentioned the place of issuance, day of the month and year of the pope's pontificate on which issued, and signatures, near which was attached the seal.
For the most solemn bulls, the pope signed the document himself, in which case he used the formula "Ego N. Catholicae Ecclesiae Episcopus" ("I, N., Bishop of the Catholic Church"). Following the signature in this case would be an elaborate monogram, the signatures of any witnesses, and then the seal. In modern times, a member of the Roman Curia signs the document on behalf of the pope, usually the Cardinal Secretary of State, and thus the monogram is omitted.