Free Content
Free content encompasses all works in the public domain and also those copyrighted works whose licenses honor and uphold the freedoms mentioned above. Because the law by default grants copyright holders monopolistic control over their creations, copyrighted content must be explicitly declared free, usually by the referencing or inclusion of licensing statements from within the work.
(Work in the public domain cannot be licensed because, by definition, its copyright has expired or has been relinquished. However, such a work is still considered free content, because it may be used for any purpose whatsoever--except, naturally, being re-copyrighted.)
Free content licenses
Free content licenses may be copyleft—in which case modifications of the work must themselves be distributed only under the terms of the original free license—or else they are non-copyleft, which means that the licensed work may be modified and then distributed under a different license, even one that is less free.
Most free content licenses contain provisions specifying that derivative works must attribute or give credit to the authors of the original, a requirement which promotes intellectual honesty and discourages plagiarism without imposing so great a burden as to weaken the claim of such licenses to being truly free.
The Design Science License (DSL), and GNU Free Documentation License (GFDL) are copyleft licenses for free content. The FreeBSD Documentation License is an example of a non-copyleft license. The GNU General Public License (GPL) can also be used as a free content license. Against DRM license is a free copyleft license for artworks published by Free Creations.
Other examples of free content licenses are some of those published by Creative Commons when commercial use and derivative works are not restricted, although they do not require a source copy of the license be provided. Note that not all Creative Commons licenses are free content as defined here. The Libre Society project also has some free content licenses and a critique of the Creative Commons philosophy.
It is questioned whether the IANG license complies with the definition of free content given here, since it puts responsibilities on redistribution the product, notably by requiring access to financial accounting.
All text of this article available under the terms of the GNU Free Documentation License (see Copyrights for details).