The expression copyleft (sometimes indicated in Italian with "copyright permission") indicates a model of copyright management based on a system of licenses through which the author (as the original holder of the rights on the work ) indicates to the users of the work that it can be used, disseminated and often even modified freely, while respecting some essential conditions. Copyleft (copyright permission) can be applied to a multitude of works, ranging from software to literary works, from videos to musical works, from databases to photographs.
In the pure and original version of the copyleft (i.e. the one referring to the IT environment) the main condition obliges the users of the work, if they want to distribute the modified work, to do so under the same legal regime (and generally under the same license) . In this way, the copyleft regime and the whole set of freedom deriving from it are always guaranteed at each release.
This terminal, in a not strictly technical-legal sense, can also generally indicate the cultural movement that has developed on the wave of this new practice in response to the stiffening of the traditional copyright model.
Examples of copyleft licenses for software are the GNU GPL and the GNU LGPL, for other areas the Creative Commons licenses (more properly with the share alike clause) or the same GNU FDL license used for Wikipedia up to 2009 (date of transition to the license Creative Commons).
The term copyleft, according to some sources, came from a message contained in the Palo Alto Tiny BASIC, a free version of the BASIC language written by Li-Chen Wang in the late 1970s and derived from Tiny BASIC. The listing of the programs contained the phrases "@COPYLEFT" and "ALL WRONGS RESERVED", puns on "copyright" and "all rights reserved" (all rights reserved), a phrase commonly used in the declarations of copyright.
Richard Stallman states that the word comes from Don Hopkins, who sent him a letter in 1984 or 1985, in which it was written: "Copyleft - all rights reversed." (Copyleft - all rights reversed.)
The expression is a play on the term copyright, in which the word right, which means "right" (in the legal sense), is reversed with left, which means "sold"; playing on the second meaning of the words, you can see how right (ie "right") is exchanged with left ("left") also in the logo. Also left is the past participle of the verb to leave, which means "to leave", "to abandon": in this way there is a further pun on releasing the rights instead of reserving (seli), although Stallman rejects this interpretation.
Some read in the word left a reference to cultural circles that traditionally fight against copyright - that is, those of the left - in aversion to those who traditionally defend them - those of the right. Stallman's political activism contributed to this interpretation.
At the beginning of the seventies the term copyleft with the notation "All Rights Reversed" was used in the Principia Discordia, the pronunciation of which resembles "All Rights Reserved"; the literal meaning is All rights reversed, but has a sound similar to the phrase All rights reserved (with the exception of reversed, which is also an anagram of reserved. This may have been the source of inspiration for Hopkins or others) .
There are problems in defining the term "copyleft" due to the controversy that characterizes it. The term, created as a fascinating counterpart to the term "copyright", originally a noun, indicates the type of license published under the GNU General Public License devised by Richard Stallman as part of the work of the Free Software Foundation. So "your program is cop