What is the GNU General Public License (GPL) and how does it work?

The GNU General Public License (GPL) is a widely used free software license that was created by the Free Software Foundation (FSF). It is designed to ensure that software remains free and open source, allowing users to use, modify, and distribute the software freely.

The GPL operates on the principle of copyleft, which means that any derivative work or modifications made to the original software must also be licensed under the GPL. This ensures that the software and its derivatives remain free and open source, preventing anyone from restricting the rights of others to use, modify, and distribute the software.

Under the GPL, users are granted four essential freedoms:

1. The freedom to run the software for any purpose.
2. The freedom to study and modify the source code of the software.
3. The freedom to distribute copies of the software.
4. The freedom to distribute modified versions of the software.

To comply with the GPL, when distributing software under this license, the source code must be made available to recipients, allowing them to study, modify, and distribute the software further. This ensures that the software remains accessible and modifiable by the community.

The GPL also includes provisions to prevent the addition of additional restrictions on the software. It prohibits any licensing terms that would restrict the rights granted by the GPL, such as adding restrictions on the distribution of modified versions or charging royalties for the software.

One important aspect of the GPL is its compatibility with other licenses. If a program is licensed under the GPL, it can be combined with other GPL-licensed software or software licensed under compatible licenses, such as the GNU Lesser General Public License (LGPL). However, it cannot be combined with software licensed under incompatible licenses, such as proprietary licenses.

In summary, the GNU General Public License (GPL) is a free software license that ensures software remains free and open source. It operates on the principle of copyleft, granting users the freedom to use, modify, and distribute the software and its derivatives. Compliance with the GPL requires making the source code available and prohibits the addition of additional restrictions on the software.