Does it mean I can use royalty free sound and image files in my games I sell? If not what if the license states that I can use those free resources in commercial games?
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Royalty free means that you don't have to pay a percentage (a royalty) for each use of the resource. How you may or may not use it is in the licence.
But always read the license.. Usually any royalty free asset (sound, image or templates) allows only 1 use for comercial projects. And you need to buy it again for another project.