The concept of copyleft is an implementation of the copyright. It arose with the purpose of protecting the free circulation of the computer code and the knowledge it contains. Use copyright law to protect freedom of copying, modification, and redistribution, rather than restricting it.
A definition of copyleft would be the system that allows the free distribution of copies and modified versions of a work or work, claiming that the same rights are respected in the different versions that are changed. In principle, copyleft licenses can be used for computer programs, science, culture, works of art or any creative work that is governed by copyright.
Examples of copyleft include, for example, modifications and copies that can be made of a painter's works of art or changes to a computer program to improve it.
This concept appears in the free software communities as a play on words linked to the term copyright (copyright or copy right). In English copyleft would be translated as 'left of author', although in this case, left is associated with the past tense of the verb allow or leave. A free license is copyleft when, in addition to providing permissions for copying, uses, exchange and redistribution of the protected work, it has a clause that has a license similar or compatible to copies and linked works. Therefore copyleft and copyright are two different types of rights.
Types of copyleft
There are basically four kinds of copyleft that you should know about:
- Strong copyleft: when the derivative works of a program cannot be linked by non-free programs. However, this does not prohibit the opposite, that a strongly copyleft program links to a proprietary one. What it wants is not to give facilities to proprietary software developers.
- Weak copyleft: allows derivative works of a program to be linked by non-free programs.
- Complete copyleft: it is when the derivative works of a program have to be distributed under the same conditions as the original program.
- Partial copyleft: refers to when the works from a program should be distributed only the edited part, with the same conditions as the original.