A more thorough explanation:

REGISTRUM BREVIUM

Registrum brevium is a Latin term that refers to the register of writs.

It is an official record of legal documents that contain instructions from a court or a judge to take a specific action.

The abbreviation for registrum brevium is reg. brev.

One example of a registrum brevium is a writ of habeas corpus, which is a legal order that requires a person who is being detained to be brought before a court or a judge.

Another example is a writ of mandamus, which is a legal order that requires a public official or a government agency to perform a specific duty.

These examples illustrate how registrum brevium was used to keep a record of important legal documents that were issued by courts and judges.