Messages

     (object-oriented) A message is the way an object is requested to perform
     some action.  Messages are sent to an object and composed of the object
     name, the send operator, and the selector name followed by arguments
     enclosed in parentheses.  The selector has the same name as the method
     it is calling.  Sending a message produces a return value, much like a
     function call with the return value varying depending on the operation
     performed.