A more thorough explanation:

Definition: Letters secret refers to a document issued by the government to a private person that is sealed and not available for public inspection. It is also known as letters close.

Example: A letter secret could be a confidential agreement between a government and a private company. The contents of the document are not available to the public, and only the parties involved have access to it.

Explanation: The example illustrates how letters secret are used to keep certain information confidential. In this case, the government and the private company have agreed to keep the details of their agreement private, and the letters secret document ensures that the information is not made public.