Hi,
Maybe you are talking about Public domain. A lot of classical music compositions are in the public domain, I am talking about the composition not about the recording. Depending on the country where the composer is from, his music compositions will be in the public domain 70 years after his death (in some countries it's 50 years, in others more..), but this doesn't mean that you can use a Chopin piano recording and use it for free in your production.
The composition is in the public domain, so you can make your own version and own recording and use it wherever you want.
In the recording there is other rights: producer rights, musicians rights, publisher rights..so the composition can be in the public domain and the recording not.
Royalty free music is another subject, this term is related to music tracks that are nor managed by Performance rights organizations such BMI, SACEM..
When a filmmaker want to use a music track in his film (for example) he will pay a series of fees for the use of the music, (to the composer, the publisher, the producer...etc) and additional fees for each public performance.
If a royalty free music is used, the filmmaker (or any user) pay once for all the necessary rights (including all performances). There is many royalty free music providers:
http://freemusicarchive.org/
https://www.musicscreen.org/