Copyright and the Public Domain
Authors own the exclusive rights to their compositions. This is called a copyright, and the composition is protected for many years--even if the copyright is never registered with the copyright office. A composition is considered to be "intellectual property" The copyright may be sold, transferred, or inherited--but the copyright still endures. If any music or lyrics are still under copyright protection
Fortunately, copyrights eventually expire and the owner no longer has no exclusive rights. All compositions not protected under copyright law are said to be in the public domain. A work is in the public domain when no one on this entire planet can find any law which gives them legal claim to a property. Public domain is the complete absence of any law allowing ownership of a property. If you can prove that a composition is in the public domain, you can use the work any way you can imagine. You can arrange, reproduce, perform, record, publish it, and use or sell it commercially as you like.
Musical Works and Sound Recordings
A Musical Work and a Sound Recording of a Musical Work have separate and extremely different copyright protection.
For example, The children's song, "Mary Had A Little Lamb" is absolutely in the public domain worldwide, and it can be freely used by anyone. However, in the USA, no sound recordings of "Mary Had A Little Lamb" are in the public domain.
Rule of Thumb for Public Domain Music and Sound Recordings