Creative Commons licenses allow a creator to designate a wide range of acceptable uses for their work. The basic condition in all of the CC licenses is attribution - The user must provide credit to the creator (and certain other information such as where the original work may be found).
Allows use of the work for any purpose as long as attribution is given to the creator.
Allows use of the wok for any purpose as long as attribution is given and adaptations are shared under the same license.
Allows non-commerical use of the work as long as attribution is given to the creator.
Allows non-commerical use of the work as long as attribution is given and adaptations are shared under the same license.
Allows use of the work without adaptations as long as attribution is given to the creator.
Allows non-commercial use of the work without adaptations as long as attribution is given to the creator.
In addition to the Creative Commons Licenses which reserve some rights for the creator, there are two public domain tools which indicate materials in the public domain, not subject to copyright restrictions.
Allows the creator to dedicate their work to the public domain
"No Known Copyright" - Used to label works known to be in the public domain, free of copyright restrictions. Often used with older works.