Stand-alone applications are those that contain the main routine for the application and make API calls to access Maya in batch mode. They are compiled in a slightly different manner than plug-ins (as covered in Using a debugger to debug your plug-ins), but utilize the same API as plug-ins, and in the same way.
If these variables are not set, you will get errors when you attempt to start a stand-alone application.
The following sample applications are provided to demonstrate how to create and use stand-alone applications.