Hi! It's a Royalty-Free License. I'll quote the content here:
"CAPABILITIES
1. You can use, copy, adapt, modify, prepare derivative works based upon all purchased pq_pixels assets;
2. You may use game assets as many times as you like;
3. You can sell and distribute games, or other products, with the purchased assets.
FORBIDDEN
1. Distribution of source files is NOT permitted;
2. You can NOT resell the source files (PNG, JPG, EPS, Adobe Illustrator, etc.) or a slightly modified version of the art.
3. You can not redistribute the art or a modified version of the art in a manner that would make some or all of the art files useable to another end user via the app.
For example, an app that uses the art as part of the game is fine. An app that allows the user to save or export a modified version of the artwork itself is not fine.
Credit is not required but appreciated."