Hello,

An interesting read can be found at MVC Pattern.

In short:

Model

The Model handles the state of the application. The Model does not know anything about HTML, or web servers or anything like that.

View

The View is the representation of the user interface. In web based MVC systems, a view can be implemented using a template that renders an HTML page.

Controler

The Controller handle the incoming HTTP requests. The Controller receives user requests, and translates them into actions that the Model should take. Then it selects the appropriate View to handle the response.

Catalyst uses the MVC pattern. Mason can do the templating (as noted by the orginal poster). More can be found by googling.