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GNU Free Documentation License
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GNU Free Documentation License

The GNU Free Documentation License (GFDL) is a copyleft license for free content, designed by the Free Software Foundation (FSF) for the GNU project. The official text of version 1.2 of the license text can be found at http://www.gnu.org/copyleft/fdl.html.

The license is designed for software documentation and other reference and instructional materials. It stipulates that any copy of the material, even if modified, carry the same license. Those copies may be sold but, if produced in quantity, have to be made available in a format which facilitates further editing. Wikipedia is the largest documentation project to use this license.

Many people and groups, notably the Debian project (based on their Debian Free Software Guidelines), consider the GFDL a non-free license, due to both the usage of "invariant" text that cannot be modified or removed, and the well-meaning but overly-broad prohibition against digital rights management (DRM) systems which affects valid usages as well. See the documents in the "External links" section for more information.

Table of contents
1 Secondary Sections
2 Materials for which commercial redistribution is prohibited
3 Related articles
4 External links

Secondary Sections

The license explicitly separates any kind of "Document" from "Secondary Sections", which may not be integrated with the Document, but exist as front-matter materials or appendices. Secondary sections can contain information regarding the author's or publisher's relationship to the subject matter, but not any subject matter itself. While the Document itself is wholly editable, and is essentially covered by a license equivalent to (but both-ways incompatible with) the GNU General Public License, some of the secondary sections have various restrictions designed primarily to deal with proper attribution to previous authors.

Specifically, the authors of prior versions have to be acknowledged and certain "invariant sections" specified by the original author and dealing with his or her relationship to the subject matter may not be changed. If the material is modified, its title has to be changed (unless the prior authors give permission to retain the title). The license also has provisions for the handling of front-cover and back-cover texts of books, as well as for "History", "Acknowledgements", "Dedications" and "Endorsements" sections.

Materials for which commercial redistribution is prohibited

Materials for which commercial redistribution is prohibited generally cannot be used in a GFDL-licensed document, e.g. a Wikipedia article, because the license does not exclude commercial re-use. However in some specific cases, commercial re-uses may be fair use and in that case such materials do not need to be licensed to fall within the GFDL if such fair use is covered by all potential subsequent uses. One good example of such liberal and commercial fair use is parody.

Related articles

External links

Here are resources discussing the appropriateness of the GFDL: