Article 1, Section 8 of the U.S. Constitution states: "The Congress shall have power...To promote the progress of science and useful arts, by securing for limited times to authors and inventors the exclusive right to their respective writings and discoveries..."
Creative Commons is a nonprofit organization that enables the sharing and use of creativity and knowledge through free legal tools. Creative Commons licenses are not an alternative to copyright. They work alongside copyright and enable you to modify your copyright terms to best suit your needs.
-- Creative Commons website
The licenses and their description are from the "About the Licences" page of Creative Commons.
The 5R's of OER
The term "open content" describes any copyrightable work that is licensed in a manner that provides others with free and perpeptual permission to engage in the 5R activities:
Source: The 5R's of OER