Free license

A free license may not prohibit changing content or restrict commercial use. It can be copyleft or permissive.

There are free licenses for art/media and free licenses for software/source code.

Free art/media licenses are listed here: Definition of Free Cultural Works' license list
Free software/source code licenses are listed here: GNU Project's list of GPL-compatible licenses

About free licenses

A copyleft license requires derivate works to be licensed under the same license.

A permissive license allows all kinds of use but can require attribution.