Royalty-free stock photography is a collection of images available for use without incurring fees each time the image is used. Royalty-free does not mean the stock photography is free of cost; the user still has to pay an initial fee for the ability to use the image.
A royalty-free image can be used multiple times; however, there is usually a limit after which the buyer needs to purchase rights again. There is no time limit on how long the buyer has rights to the image. The opposite of royalty-free stock photography is rights-managed stock photography, which includes limits on types of use, duration of use and geographical location of use.