What exactly is a project in product licensing?

I am working on my own online shop where I want to sell prints from my photos. Therefore I want to use mockups and place my photos in it.

I’m not quite sure how a project is defined and what single use means exactly. Do I have to re-license the mockup every time I use the same mockup for different products (prints) in the same online store? Or only if I use it for example in a new online store?

Thanks for your help!