Creative Commons Licence
A Creative Commons Licence allows authors, artists, and educators to mark their creative work with the freedoms they want it to carry, changing the default of “All Rights Reserved” into “Some Rights Reserved”, as the creator chooses.
There are three areas that the licence covers; attribution, commercial use and derivatives. These can be combined in various way to form a licence. Creativecomms.org has more information.
The Creative Commons website also has a useful Choose A Licence page.