A more thorough explanation:

A messenger is someone who delivers a message or communication. This can include delivering telegrams or other important messages.

In the past, a messenger could also be an officer who had certain duties, such as taking care of assets in an insolvent estate.

For example, if you send a letter to a friend through the mail, the postal worker who delivers the letter is acting as a messenger. Similarly, if a company needs to send an urgent message to an employee, they may hire a messenger service to ensure the message is delivered quickly and securely.