What is GNU GPL?

The GNU General Public License was first published in 1989 by Richard Stallmann, co founder of the GNU Project. In 1991, the second version GNU GPLv2 and in 2007 the last current version GNU GPLv3 were published. The license ensures the right to for free use and modification without the developers being denied the authorship. This is usually done by placing a copy of the official GNU license text attached to the software. So every GPL license gives a lot of rights like to reproduce, distribute, modify and make the software publicly available. Therefore the publisher must also make the source code publicly available. The most well-known software, which were under this license, are Linux and WordPress.
For example you have the following rights by using WordPress :

• Everyone has the freedom to use WordPress for any purpose he or she likes.
• Everyone has the freedom to examine the WordPress source code and customize it to their own needs.
• Everyone has the freedom to copy and redistribute WordPress at will.
• Everyone has the freedom to improve WordPress and share these community improvements so everyone benefits.

If WordPress were a country, our Bill of Rights would be the GPL because it protects our core freedoms.Matt Mullenweg, Co-Founder of WordPress

And addition to rights created by GNU GPL, the GPL also sets obligations that licensees must consider if they wish to use their rights. One of the most important is known under the name Copyleft.

Copyleft

Copyleft is a clause contained in GPL that ensures that any software derived from the original must carry the same license as the original version. This means that any derived or modified version of GPL software if it´s accessible for the public, must also have the same GPL license. Based on copyright, the Copyleft symbol looks exactly the same, just upside down.
This makes it possible for “Md Asik Resources” to distribute overpriced plugins and themes for a small fee and make them available to people on a low budget. Fees we receive are spent on acquiring new plugins and themes, thereby expanding our offerings. Our philosophy is to help WordPress developers, who run on a low budget or don´t need professional support, remove all obstacles to developing professional websites. A WooCommerce online shop can costs with all themes, plugins, and extensions sometimes up to ₹ 10,000 per year.