The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the freedom to run, study, share, and modify the software. ... GPL was the first copyleft license for general use.

How does the GPL work?

The GPL is a free software license, and therefore it permits people to use and even redistribute the software without being required to pay anyone a fee for doing so. You can charge people a fee to get a copy from you. You can't require people to pay you when they get a copy from someone else.

What is the GPL why is it important?

GNU General Public License

The main reason is that the GPL compels a user to make the source code available when distributing any copies of the software, and that all modifications to the original source are also licensed under the GPL.