The Free On-line Dictionary of Computing (30 December 2018):
General Public License
GNU General Public License
(GPL, note US spelling) The licence applied to most
software from the Free Software Foundation and the GNU
project and other authors who choose to use it.
The licences 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.
See also General Public Virus.