What is Copyleft?

Copyleft is a manner of ensuring that a work will remain free in all variations and interpretations that may become of it. The term originated from the need of software developers to publish the code of their programs for others to use, yet to require those who use the code to republish the modified code and to give credit to the original programmer. The Copyleft concept was originated by the GNU Project, sponsored by the Free Software Foundation.

The term Copyleft is a play on the term copyright, which the GNU Project claims has the purpose of restricting a users' rights to the software that he acquires. In contrast, Copyleft is designed to maintain and protect a user's rights. Two freedoms are usually associated with Copyleft: the freedom to acquire the software without paying for it, and the freedom to modify and redistribute the software. These two freedoms are often referred to as "free as in beer", and "free as in speech". Most copylefted works are released under the traditional GPL licence. However, debate has been building in recent years as to the validity of the license, and there are now several licences to choose from. Most of these licences have been officially translated into many different languages, although the original English translation is intended to be the licence used in court if the need arises.

Common copylefted software include Mozilla's Firefox web browser, the Open Office suite of productivity tools, and the GNU/Linux operating system. In addition, the entire Wikipedia website is copylefted, including the source code of the operating system that runs the server, the webserver software itself, the programs that create the webpages, and the content of the webpages.