Creative Commons (CC) is the forefront non-profit organization promoting free culture, i.e. basically relaxation of "intellectual property" (such as copyright) in art. One of the most important contributions of the organization are the widely used Creative Commons licenses which artists may use to make their works more legally free and even put them to the public domain.
Creative commons licenses/waivers form a spectrum spanning from complete freedom (CC0, public domain, no conditions on use) to complete fascism (prohibiting basically everything except for non-commercial sharing). This means that NOT all Creative Commons licenses are free cultural licenses -- this is acknowledged by Creative Commons and has been intended. Keep in mind that as a good human you mustn't ever use licenses with NC (non-commercial use only) or ND (no derivatives allowed) clauses, these make your work non-free and therefore unusable.
Here is a comparison of the Creative Commons licenses/waivers, from most free (best) to least free (worst):
|Creative Commons Zero||CC0||yes :)||yes :)||yes :)||yes :)||no :)||no need :)||no :)||public domain, copyright waiver, no restrictions, most freedom, best, sadly doesn't waive patents and trademraks|
|Creative Commons Attribution||CC BY||yes :)||yes :)||yes :)||yes :)||no :)||forced :(||no :)||no restrictions except for requiring attribution to authors|
|Creative Commons Sharealike||CC SA||yes :)||yes :)||yes :)||yes :)||yes :/||no need :)||no :)||retired, secret license, no longer recommended by CC, pure copyleft/sharealike without forced attribution|
|Creative Commons Attribution Sharealike||CC BY-SA||yes :)||yes :)||yes :)||yes :)||yes :/||forced :(||no :)||requires attribution to authors and copyleft (sharing under same terms)|
|Creative Commons Attribution NonCommercial||CC BY-NC||NO! :(((||yes but||yes but||yes but||yes :/||forced :(||yes :(||proprietary fascist license prohibiting commercial use, DO NOT USE|
|Creative Commons Attribution NoDerivs||CC BY-ND||NO! :(((||yes but||yes but||NO! :(||yes :/||forced :(||no but||proprietary fascist license prohibiting modifications, DO NOT USE|
|Creative Commons Attribution NonCommercial NoDerivs||CC BY-NC-ND||NO! :(((||yes but||yes but||NO! :(||yes :/||forced :(||yes :(||proprietary fascist license prohibiting commercial use and even modifications, DO NOT USE|
|none (all rights reserved)||NO! :(((||NO! :(||NO! :(||NO! :(||FUCK YOU||FUCK YOU||FUCK YOU||proprietary fascist option, prohibits everything, DO NOT USE|
All content available under CC0 1.0 (public domain). Send comments and corrections to drummyfish at disroot dot org.