What’s the difference between papal BULL and papal BREVE?

A bull was a particular type of charter or formal document issued by a pope. Such documents were issued for many kinds of communication of a public nature, but after the 15th century, only the most formal or solemn of occasions. Modern scholars have retroactively used the term BULL to describe any elaborate document issued in the form of a decree or privilege (solemn or simple) and to some elaborate ones issued in the form of a letter. Popularly, the name bull is used to designate any papal document that includes a lead medal seal with cords or other precious metal seal (the latter are very uncommon). Any subject may be treated in a bull and many were and are including statutory decrees, episcopal appointments, dispensations, excommunications, apostolic constitutions, canonization’s, etc. A BREVE became the more common practice in the 17th to modern centuries. This document, often on parchment, was headed with the name of the pope but was signed on behalf of the pope by a senior member of his household or Roman curia. While not as desirable as papal bulls, depending upon their content and condition, may breves contain important historical information and are desirable as such.