A more thorough explanation:

Definition: Apertum breve is a type of writ that is open and unsealed. It is used in legal proceedings to communicate a message or order.

Example: An example of apertum breve is a notice from a court to appear for a hearing. The writ is not sealed and can be read by anyone who handles it.

This type of writ is different from a sealed writ, which is called a "clausum breve." A sealed writ is closed and can only be opened by the intended recipient.

Overall, apertum breve is a legal term that refers to an open and unsealed writ used in legal proceedings.