2. “To which bulls do you refer?”
A bull is a type of public decree issued by a pope, the bishop of Rome. It is named after the leaden seal (bulla) that was traditionally appended to the end in order to authenticate it.
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. Popularly, the name is used for any papal document that contains a metal seal.
Today, the bull is the only written communication in which the pope will refer to himself as "Episcopus Servus Servorum Dei" ("Bishop, Servant of the Servants of God"). For example, when Pope Benedict XVI issued a decree in bull form, he began the document with "Benedictus, Episcopus, Servus Servorum Dei”.