It’s the most affordable and most popular license type for stock photos. Royalty-Free images are NOT FOR FREE. The “Free” in Royalty-Free means you don’t have to pay extra royalties, other than the initial license fee.
RF is a one-time, flat-rate license fee. That entitles you to use the image multiple times, in a wide range of permitted uses, and forever, without ever paying extra royalties. Pay once, use forever. Simple as that.
(Be aware this license type is that all RF images are non-exclusive – anyone can purchase a license and use them.
If you need exclusive use of any of my images please contact me to discuss a custom licence.)