A more thorough explanation:

Definition: Rogatory letters are formal requests from one country's court to another country's court for assistance in obtaining evidence or serving process in a legal matter. They are also known as letters of request.

Example: In a criminal case, a prosecutor in the United States may need to obtain evidence from a witness who lives in France. The prosecutor would send a rogatory letter to the French court, requesting that they assist in obtaining the evidence.

Explanation: The example illustrates how a rogatory letter is used to request assistance from a foreign court in obtaining evidence. The letter is a formal request that must be approved by the foreign court before any action can be taken. Rogatory letters are an important tool in international legal proceedings, allowing courts to work together to ensure justice is served.