GPL has a very specific meaning – it is the acronym for General Public License. Sometimes, GPL is also called GNU GPL. GPL is a type of software license, and is the most frequently used software license for free software. Richard Stallman of the “Free Software Foundation” wrote the GPL license for the GNU Project. Software under the GPL license is completely free to be used, changed or distributed by anyone as they wish.
A popular piece of software under GPL is WordPress – anyone is able to use, change or distribute WordPress as they wish. Interestingly, the people behind the WordPress project thinks of GPL a but like the US Bill of Rights, because GPL provides to WordPress an important list of values to which the WordPress project subscribes.
These values include the ability of anyone to be able to download and to execute WordPress – and to modify it as they wish. The GPL license also implies that anyone can distribute a free copy of WordPress if they want to do so, while GPL also means that anyone can modify WordPress and then distribute this modified version of WordPress.
GPL has an important element: it is something called “copyleft”. It might remind you of the word copyright, and that’s intentional – both are similar in concept. Copyleft deploys copyright law to ensure that a modified version of a work is protected. For example, any work that uses WordPress as a basis will also effectively pull across the GPL license.
It is an aspect of GPL that can lead to controversy as some commercial operators have gone ahead and tried to sell their plugins and themes for WordPress under a license which is not compliant with GPL. Nonetheless, the WordPress community has very strong views on its bill of right aka GPL – and acts to protect this bill of rights. Matt Mullenweg who played a key part in the founding of WordPress has actively expressed his view on the topic.