Royalty-Free Music/SFX doesn't mean that the music/SFX is free to use, but rather that as the Licensee, you are not responsible for paying royalties to the owners/composers of that music. This allows you to use services such as Slip.Stream to get high-quality music/SFX for your projects without worrying about having to pay the artist we take care of everything for you.
What is Royalty-Free Music?
This article described what royalty-free music is and how it works.

Written by Brandon Seekins
Updated over a week ago
Updated over a week ago