Explanation: In a non-legal sense, copyleft, a play on the word copyright, is the opposite of copyright. Copyleft refers to the practice of using copyright law to remove restrictions on the distribution of copies and modified versions of a work for others and require the same freedoms be preserved in modified versions. A widely used copyleft license is the GNU General Public License (GPL). Many fans of copyleft media believe that copyleft is a cross between copyright and public domain.
Other definitions in programming such as Copyleft in Dictionary C.