"Creative Commons is a global nonprofit organization that enables sharing and reuse of creativity and knowledge through the provision of free legal tools." https://creativecommons.org/faq/#what-is-creative-commons-and-what-do-you-do
For more information, check out the following links:
There are six different license types, listed from most to least permissive here:
CC BY includes the following elements:
BY – Credit must be given to the creator
CC BY-SA includes the following elements:
BY – Credit must be given to the creator
SA – Adaptations must be shared under the same terms
It includes the following elements:
BY – Credit must be given to the creator
NC – Only noncommercial uses of the work are permitted
CC BY-NC-SA includes the following elements:
BY – Credit must be given to the creator
NC – Only noncommercial uses of the work are permitted
SA – Adaptations must be shared under the same terms
CC BY-ND includes the following elements:
BY – Credit must be given to the creator
ND – No derivatives or adaptations of the work are permitted
CC BY-NC-ND includes the following elements:
BY – Credit must be given to the creator
NC – Only noncommercial uses of the work are permitted
ND – No derivatives or adaptations of the work are permitted
CC0 (aka CC Zero) is a public dedication tool, which allows creators to give up their copyright and put their works into the worldwide public domain. CC0 allows reusers to distribute, remix, adapt, and build upon the material in any medium or format, with no conditions.
Source: CreativeCommons.org