" bulls from a dead pope"
Papal bull of Pope Urban VIII. 1637. Sealed with a leaden bulla
Public DomainPapal bull of Pope Urban VIII. 1637. Sealed with a leaden bulla - Credit: Wikimedia Commons

Papal bulls are official charters issued by the Pope.

Before the 15th century they were issued for a wide variety of matters, but since then they have been reserved for only the most serious or solemn of occasions. The term 'bull' is taken from the bulla that appends the document -- the metal seal that authenticates it.