Free music can also mean free improvisation: improvised music without any rules, and not in any particular style.
For information on swapping of (non-free) music see File sharing, Napster or eMule.
Free music or libre music is music that, like free software, can freely be copied, distributed and modified for any purpose. Thus free music is either in the public domain or licensed under a free license by the artist or copyright holder themselves, often as a method of promotion. It does not mean that there should be no fee involved. The word free refers to freedom (as in free software), not to price.The Free Music Philosophy generally encourages creators to free music using whatever language or methods they wish. A Free Music Public License (FMPL) is available for those who prefer a formal approach.
Some free music is licensed under licenses that are intended for software (like the GPL) or other writings (the GFDL). But there are also licenses especially for music and other works of art, such as EFF's Open Audio License, LinuxTag's Open Music License, the Free Art license and some of the Creative Commons Licences.