"Creative Commons licenses let content creators keep their copyrights, but offer some conditional rights to the world to use what they've created. All Creative Commons licenses include attribution, meaning anyone using that content must give credit to the original author of the work. Then licensees can add conditions--say, allowing people to copy, distribute, display, and perform the work, but not to gain commercially, not to base other works on it, or, if derivative works are allowed, to require them to use an identical license." MacLife, January 2009
Specifics about the licenses:
Creative Commons is a nonprofit corporation dedicated to making it easier for people to share and build upon the work of others, consistent with the rules of copyright.