Copyright

Traditional Copyright

Main article: Copyright
Traditionally, copyright is a legal concept, which grants the author or creator of a work, legal rights to control the distribution and display of their work, in many jurisdictions this is limited by a time period after which the works then enter the public domain. During the time period of copyright the author's work may only be distributed, displayed or modified with the consent of the author, usually via a copyright licence.

From the perspective of free content, traditional usages of copyright is limiting in several ways. It limits the distribution of the work of the author to those who can, or are willing to, afford the payment of royalties to the author for usage of the authors content. Secondly it creates a perceived barrier between authors, which limits modification of the work, such as in the form of mashups and collaborative content.

Public Domain

Main article: Public domain
The public domain is a range of abstract materials–commonly referred to as intellectual property–which are not owned or controlled by anyone. A public domain work is a work whose author has either relinquished, or no longer can claim control over the distribution and usage of the work. As such any person may manipulate, distribute or otherwise utilise the work, without legal ramifications. A work released as public domain by its author is free and copycenter.[3]

Copyleft

Main article: Copyleft
The copyleft symbol
For how copyleft is used to provide a collaboration framework for Wikipedia, see Wikipedia:The Free Encyclopedia

Copyleft is a play on the word copyright and describes the practice of using copyright law to remove restrictions on distributing copies and modified versions of a work. The aim of copyleft is to use the legal framework of copyright to enable non-author parties to be able to reuse and, in many licencing schemes, modify content that is created by an author. Unlike public domain or other non-copyleft free work, the author still maintains copyright over the material, however the author has granted a non-exclusive license to any person to distribute, and often modify, the work. Copyleft licenses require that any derivative works be distributed under the same terms, and that the original copyright notices be maintained.