When I refer to "controller", what I am talking about is the "C" in the MVC (Model-View-Controller) design pattern.

Simplistically, this design pattern suggests that an application should be divided into three isolatable parts...

1. The presentation layer (View),
2. The data (Model) and,
3. The Controller (the business rules that take data from the presentation layer and manipulate it into the model).

This design pattern is especially effective in web applicaiton development.