In today’s world when creating and developing websites, the most popular platform is WordPress.
Administrators ,marketers ,designers and web developers can use the vast WordPress open source support for plugins and themes, by that save a lot of development time to get excellent results in a very small amount of time.
WordPress platform is a free open source platform, it has been released under the GPL license. But, in the case of some plugins and themes, there are GPL and Split Licenses (one part of the code is GPL and another is not).
“The GNU General Public License (GNU GPL or GPL) is a widely-used free software license, which guarantees end users the freedom to run, study, share and modify the software. The license was originally written by Richard Stallman of the Free Software Foundation (FSF) for the GNU Project, and grants the recipients of a computer program the rights of the Free Software Definition. The GPL is a copyleft license, which means that derivative work can only be distributed under the same license terms. This is in distinction to permissive free software licenses, of which the BSD licenses and the MIT License are widely-used examples. GPL was the first copyleft license for general use.”
In other words, GPL plugin is a free software structure which can be used, modified and distributed without any legal restrictions or limitations.
This means that once a plugin is purchased directly from the official site of its creators it can be sold, given away or used on as many sites as desired, as long as the source code remains available to its users.
Another case is the Split License, a term when the plugin’s integration with WordPress a.k.a. The PHP code is kept under GPL license, but the html code (images, text, CSS styles, photographs, etc) are released under other licenses which restrict the use of these elements according to the rights that the author determines on their intellectual property.