Copyleft
Both copyleft and non-copyleft ("permissive") licenses for free content or free software can be used for things like documents (for example books, art, music and software); they always allow people to change the works, and to give or sell them to other people. It should be noted that, although people might think that copyleft content is not copyrighted, that's a myth. Copyleft is a form of licensing: it is not just another name for public domain.