“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.”
The above definition comes from the Creative Commons website. The organization was founded in 2001 by, among others, Harvard Professor Lawrence Lessig. Its goal was to provide simple, easy to understand and use copyright licenses that would allow creators to share their work with the world under terms they were comfortable with, so people can share, remix, and/or use them commercially, rather than the default terms offered by statute. Currently, Creative Commons offers 6 different licenses (in 50 countries and counting), whose features vary according to their permissiveness, and the uses they allow. The existence and terms of these special licenses are communicated to users by employing both the Creative Commons name and a series of icons that suggest the specific terms of the license.
A 2008 U.S. case, Jacobsen v. Katzer, concerning later usage of software licensed under a license similar in style and intent to those offered by Creative Commons held that the license was a valid one, and that violating it terms constituted copyright infringement. The ruling greatly strengthened the enforceability of such agreements, helping their use to be perceived as more mainstream and legitimate.