What means "Module" in the Desk comparison table?

What means "Module" in the Desk comparison table?

We are going to expand the use of departments and blueprints on our Desk subscription. I was looking at the limitations for these points to be sure if we were going to fit into them. When I look at the feature comparison list, I can see that we are allowed to create "20 Blueprints per Module". I can't find the definition of a "module". What does it exactly mean? Is a "module" the same thing as a "department"? There are some limits which use the "department/module" definition which makes it look like that a module is a different thing than a department.