Creative Commons is both an organization, a set of licenses and a movement.
CC licenses allow creators to share their work while still retaining copyright. Copyright defaults to all rights reserved for the creator. CC licenses operate as some right reserved and allow creators to determine how they would like to share their work with other users.
For a history of the development of CC licenses check out this timeline.
There are 3 layers to a CC license:
Legal code: These are the terms and conditions that lawyers refer to and are enforceable in court.
Commons Deeds: These are the webpages that explain the license terms to the regular user and summarize the legal code.
"Machine-readable" version of the license: metadata that is attached to the license that describes it to software. This way, someone searching for a CC licensed work in Google can more easily find them.
Example of machine-readable version of a license:
The three layers of a license are like the layers of a cake:
Creative Commons Licenses Libguide by Nora Hehemann is licensed under Creative Commons Attribution-ShareAlike 4.0 International License.
"License Design and Terminology" https://certificates.creativecommons.org/cccertedu/chapter/3-1-license-design-and-terminology/ by Creative Commons. CC BY 4.0.