At the conceptual level, we often talk about message passing in between object. At the underlying, technical level this covers activation of operations - procedure or function calls - on objects.
As a metaphor, we pretend that objects communicate by means of message passing
Interacting Game, Die, and Random objects
The result sent back is an integral part of the original message - not a new message in its own right.
Read more about message passing in the text book version of this material.