The GNU General Public License is a free, “copyleft” license for software and other kinds of works in a sense that it protects the freedoms – the rights - of users of thus licensed software instead of focusing on the moral and material rights of authors within the recognized and almost universally accepted framework of copyright and neighbouring rights.

Source: Katulić, T.:” Opportunities and pitfalls of GPL software licencing agreement from the perspective of the software developer”, Central European Conference on Information and Intelligent Systems, CECIIS 2013