<a href="http://c2.com/cgi/wiki?ModelViewController" rel="nofollow">http://c2.com/cgi/wiki?ModelViewController</a> and, from there, <a href="http://c2.com/cgi/wiki?WhatsaControllerAnyway" rel="nofollow">http://c2.com/cgi/wiki?WhatsaControllerAnyway</a> give historical info and show that we cannot have a single good explanation. You will have to state which MVC you want to see explained first.