Royalty-free licenses don't require an ongoing payment for use of the work you're licensing, and are often used for licensing photographs, songs, and other media.
Does royalty-free mean free for commercial use?
An image that is royalty-free is not necessarily free for commercial use — that is, any use that could lead to buying or selling something. The most reliable image services require you to pay a fee for a license that allows you to use the image for commercial or non-commercial uses, as long as you follow the terms.
Can royalty-free music be used commercially?
Yes, you can use royalty free music for commercial uses. Royalty-free means that the purchaser of a product does not have to pay royalties after the purchase and can thus legally distribute it without permission from its creator or copyright holder (in this case musician).