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.

By the 13th century the term “papal bull' referred to only the most important documents issued by the pope. These included canonizations of saints, dogmatic pronouncements, Henry VIII's dispensation to marry Catherine of Aragon (his brother's widow), the restoration of the Society of Jesus in 1814, and the announcement (Dec. 25, 1961) of the forthcoming Second Vatican Council.