What is Message Passing in Object-oriented programming?

Objects communicate with one another by sending and receiving information much the
same way as people pass messages to one another. The concept of message passing
makes it easier to talk about building systems that directly model or simulate their real-world
counterparts.

A Message for an object is a request for execution of a procedure, and therefore will
invoke a function (procedure) in the receiving object that generates the desired results.
Message passing involves specifying the name of the object, the name of the function
(message) and the information to be sent.