What is the GNU General Public License?
Any software released under the GNU General Public License which means that its source code is freely-distributed and available to the general public. Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software–to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation’s software and to any other program whose authors commit to using it.