Wikis are often par of the free culture movement. Free content licenses allow anyone to reuse, modify, or distribute the content free of charge for any purpose as long as they adhere to the license. For example, they must attribute the original authors and keep the content under the same free license even if they change the content. Examples of free licenses include the GFDL and some of the Creative Commons Licenses. Free licenses are defined by the site at FreedomDefined.org. See also What license does Wikianswers use?