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. For more information see Free Software Foundation statements of intent.

The license of the GNU/Linux kernel, it goes the opposite way of all proprietary licenses in that it gives no restriction as to copying, modifying and redistributing the software, as long as the source code is made available. The only restriction is that the persons to whom you redistribute it must also benefit from the same rights. GUI

The licenses for most software are designed to prevent users from sharing or changing it. By contrast, the GNU General Public License is intended to guarantee the freedom to share and change free software - to make sure the software is free for all its users. The GPL is designed to make sure that anyone can distribute copies of free software (and charge for this service if they wish); that they receive source code or can get it if they want; that they can change the software or use pieces of it in new free programs; and that they know they can do these things. The GPL forbids anyone to deny others these rights or to ask them to surrender the rights. These restrictions translate to certain responsibilities for those who distribute copies of the software or modify it. Source: Foldoc: Free On-line Dictionary of Computing