Application and Module
What is this ?
The framework has a hierachie. It divides your project in an application. This application is divided into modules. The good thing with that is that you will be able to reuse your module for another application.
Application
Basically, the application is the content of your page. It contains a least one module.
Module
If you rode the MVC part, you rememeber what is a Model, a Controller and a View. So a module use this concept. It contains a model (we will call it model helper or MH) and a controller (controller helper or CH). They can interact with the full document or just a part of it (the view). We use the word helper because in fact you controller and model helper will help the main model and main controller.
Below, you can see a schema of an application with one module (CH1 and MH1) :
