Creative Commons is a nonprofit organization that enables the sharing and use of creativity and knowledge through free legal tools.
Their free, easy-to-use copyright licenses provide a simple, standardized way to give the public permission to share and use your creative work — on conditions of your choice. CC licenses let you easily change your copyright terms from the default of “all rights reserved” to “some rights reserved.”
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.
(Text taken from the Creative Commons website)