Source : Free On-Line Dictionary of Computing

copyleft
     
         /kop'ee-left/ (A play on "copyright") The {copyright}
        notice and {General Public License} applying to the works of
        the {Free Software Foundation}, granting reuse and
        reproduction rights to everyone.
     
        Typically copyrights take away freedoms; copyleft preserves
        them.  It is a legal instrument that requires those who pass
        on a program to include the rights to use, modify, and
        redistribute the code; the code and the freedoms become
        legally inseparable.
     
        The copyleft used by the GNU Project combines a regular
        copyright notice and the "GNU General Public License" (GPL).
        The GPL is a copying license which basically says that you
        have the aforementioned freedoms.  The license is included in
        each GNU source code distribution and manual.
     
        See also {General Public Virus}.
     
        [{Jargon File}]
     
        (1995-04-18)