The Latin word for seal is bulla, so originally bulle referred to the seal affixed to a document. The word came to be used to connote a letter written by the Pope (Papal bull) to which a lead bulla (Latin for seal), inscribed with the name of the pontiff, was attached by a silken cord. Each bulle (letter) was known (titled) by the first few Latin words therein. But the same words were often repeated eg for letters of excommunication: the first words were not a unique identifier for a particular letter on a specific date. Bulles were not official in France until registered at Parlement. These letters were of widely varying natures, they might be constitutions (decrees sent to all the faithful), encyclicals (guidance sent to bishops), decretals (replies to questions) or orders of excommunication.