The royalty or copyright free music is one where no one owns the copyright to the selected music and there are no obligations to pay royalties. However, the truth is that the music you plan to find, including the one that is royalty free, is overwhelmingly copyrighted. The mechanism is that you purchase a license to whatever track, even if it is royalty-free. The license allows free use of music in your videos, whereas the company you get the license from pays the royalties to the artists.