Single License
Buying a single license gives you the right to use you purchased item for one project, which could be for you or on behalf of a client.
If you buy a single app license you do not have the right to use the script for more than one project. Additionally you are not allowed to resell or distribute the script ‘as-is’, modified or as part any other collection of files.
Multiple License
The multiple license allows you to use the purchased item for an unlimited amount of projects which can be for your personal use or on behalf of a client. Similarly you can reskin, modify, adapt or translate the app template and sell it as a stand-alone app or project.