Copyleft is a play on the word copyright and describes the practice of using copyright law to remove restrictions on distributing copies and modified versions of a work.^[14] The aim of copyleft is to use the legal framework of copyright to enable non-author parties to be able to reuse and, in many licensing schemes, modify content that is created by an author. Unlike works in the public domain, the author still maintains copyright over the material, however the author has granted a non-exclusive license to any person to distribute, and often modify, the work. Copyleft licenses require that any derivative works be distributed under the same terms, and that the original copyright notices be maintained. A symbol commonly associated with copyleft is a reversal of the copyright symbol, facing the other way; the opening of the C points left rather than right. Unlike the copyright symbol, the copyleft symbol does not have a codified meaning.^[15]

Projects that provide free content exist in several areas of interest, such as software, academic literature, general literature, music, images, video, and engineering. Technology has reduced the cost of publication and reduced the entry barrier sufficiently to allow for the production of widely disseminated materials by individuals or small groups. Projects to provide free literature and multimedia content have become increasingly prominent owing to the ease of dissemination of materials that is associated with the development of computer technology. Such dissemination may have been too costly prior to these technological developments.

Media

In media, which includes textual, audio, and visual content, free licensing schemes such as some of the licenses made by Creative Commons have allowed for the dissemination of works under a clear set of legal permissions. Not all of the Creative Commons’ licenses are entirely free: their permissions may range from very liberal general redistribution and modification of the work to a more restrictive redistribution-only licensing. Since February 2008, Creative Commons licenses which are entirely free carry a badge indicating that they are "approved for free cultural works".^[16] Repositories exist which exclusively feature free material and provide content such as photographs, clip art, music,^[17] and literature,.^[18] While extensive reuse of free content from one website in another website is legal, it is usually not sensible because of the duplicate content problem. Wikipedia is amongst the most well-known databases of user-uploaded free content on the web. While the vast majority of content on Wikipedia is free content, some copyrighted material is hosted u