13. What is copyleft?

Copyleft is a characteristic a creator may want to give to a creation. That characteristic consists in lifting Intellectual Property Rights-related impediments regarding the distribution of copies and modified versions of the creation, and lifting practical impediments regarding the creation of such modified versions by others.

Most commonly, copyleft is implemented by a license defining specific copyright terms applied to works such as software, documents, music, and art. Whereas copyright law is seen by the original proponents of copyleft as a way to restrict the right to make and redistribute copies of a particular work, a copyleft license uses copyright law in order to ensure that every person who receives a copy of a work can study, use, modify, and also redistribute both the work, and derived versions of the work, where the same license terms apply to all redistributed versions of the work. Thus, in a non-legal sense, copyleft is the opposite of copyright.

Authors and developers use copyleft with their work to include others in improving and elaborating the work as a continuing process.