Definition from Wiktionary, the free dictionary
Pun on copyright.
- The philosophy of using copyrights to enforce freedom of information, especially software source code.
- They believe in copyleft because they want their software to be used freely by anyone.
- A software license that follows this philosophy.
- I have placed my program under copyleft.
- The GNU General Public License is a copyleft licence.
Derived terms 
- To license under a copyleft license.
- Linus Torvalds copylefted the Linux kernel.