An end product is one thing your users see: a client site, a SaaS app or an internal tool. One Pro license covers one of them.
- Development, staging and production copies of the same product count as one.
- Everyone working on that product can use the files.
- A second product — another client, another app — needs another license.
The Free version has no such limit: it's MIT licensed, so you can use it in as many projects as you like.