General Public License
The General Public License, or simply, GPL, pertains to a free, copyleft license for the software. What it does is grant just about anyone the right to use, read, copy, modify, and distribute a computer program or any other kind of electronic work free-of-charge. The GPL was initially meant for the GNU Project and was the first copyleft license that had been adopted for general use.
The GPL was created back in 1989 by one Richard Stallman, the founder of the Free Software Foundation (FSF). Unlike copyright, copyleft entails that the GPL allows for works that are derivatives to be duly published. While this is the case, these are still to be distributed under the same license terms as if it were the original work.