1. Copyleft (a play on the word copyright) is the practice of offering people the right to freely distribute copies and modified versions of a work with the stipulation that the same rights be preserved in derivative works down the line. Copyleft software licenses are considered protective or reciprocal, as contrasted with permissive free software licenses.
2. Copyleft is a strategy of utilizing copyright law to pursue the policy goal of fostering and encouraging the equal and inalienable right to copy, share, modify and improve creative works of authorship
https://en.wikipedia.org/wiki/Copyleft (1.); https://copyleft.org/ (2.)
Author: Markus Jödicke