Also found in: Dictionary, Thesaurus, Medical, Legal, Financial, Acronyms, Wikipedia.


/kop'ee-left/ (A play on "copyright") The copyright notice and General Public License applying to the works of the Free Software Foundation, granting reuse and reproduction rights to everyone.

Typically copyrights take away freedoms; copyleft preserves them. It is a legal instrument that requires those who pass on a program to include the rights to use, modify, and redistribute the code; the code and the freedoms become legally inseparable.

The copyleft used by the GNU Project combines a regular copyright notice and the "GNU General Public License" (GPL). The GPL is a copying license which basically says that you have the aforementioned freedoms. The license is included in each GNU source code distribution and manual.

See also General Public Virus.
This article is provided by FOLDOC - Free Online Dictionary of Computing (


A requirement in the GNU GPL software license and other "free" software licenses that anyone who redistributes the software does so under the same license and also includes the source code. The "free" means free of restrictions (see free software). The copyleft clauses were written to support copyright laws, not eliminate them.

Strong vs. Weak
A "strong copyleft" license, such as the GNU GPL license, applies to all derived works and software components in the package. A "weak copyleft" license, such as the GNU Lesser GPL, applies only to the original copylefted work.

Full vs. Partial
"Full copyleft" means that all of the work may be modified, whereas "partial copyleft" restricts some parts of the work from being altered. See GNU General Public License and copyright.
Copyright © 1981-2019 by The Computer Language Company Inc. All Rights reserved. THIS DEFINITION IS FOR PERSONAL USE ONLY. All other reproduction is strictly prohibited without permission from the publisher.
References in periodicals archive ?
Stallman: When free programs are copylefted, nobody can legally make non-free versions of them.
To stop the industry from appropriating bits of the free code and integrating them into non-public, industrial products, Stallman invented the concept of Copyleft and the GPL (General Public Licence) by which the author of a software programme would allow everybody to copy, modify and distribute it, on condition that they would not prevent others from doing the same.
(108.) If feasible, two or three copyleft options would be desirable, given the variety of options that have developed in the area of free software.
No, it's not possible to make as much money as a proprietary company can--open source and copyleft will ensure this--and there's always going to be an astounding amount of work that has to be done without financial reward.
This sharing (also known as Copyleft) is designed to create a software ecosystem where all changes, modifications and additions are provided to the community instead of being kept proprietary and closed.
However, based on its reception by the members of this list and the greater open source community, the community consensus required to support OSI approval does not currently appear to exist regarding the copyleft provision of SSPL.
Some licenses, such as the GNU General Public License v3.0, may require you to publish your amended version under a similar license--this is known as a 'copyleft' license.