Creative Commons is a non-profit (under the US tax code, a 501(c)(3)) organisation that was created by Lawrence Lessig and is best known for creating licenses which can be used by creators of content to make it copyleft - that is, subject to copyright but under a looser set of rules that encourage reuse. This makes it similar to the sort of licenses used for free and open source software such as the GNU General Public Licenses and the MIT/BSD licenses, but designed for creative works such as written texts, photographs and visual artworks, films, videos, musical scores, musical recordings and multimedia.
Creative Commons provides licenses that have a variety of restrictions which can be combined together. These restrictions are as follows:
- Attribution - must provide reasonable attribution of original creator.
- Share Alike - modifications must be released under the same license conditions as the original.
- Non-Commercial - cannot be used commercially
- No Derivations - cannot be combined with other work
Obviously, Share Alike and No Derivations cannot be combined, but otherwise authors can choose which of these restrictions apply to their work.
Some have expressed concerns about exactly what Non-Commercial and Attribution entails.