Public Domain Mark: Free of known copyright restrictions due to the age of the work or federally-authored work.
Public Domain Zero License: The author has intentionally waived their copyright.
BY (Attribution): You must give appropriate credit to the creator, provide a link to the license, and indicate if changes were made.
SA (Share Alike): You may modify the original work but must publish the modifications under the original license.
NC (Non-Commercial): You may not use the material for commercial purposes.
ND (No Derivatives): No derivatives or adaptations of the work are permitted.
The licenses above may be combined to expand or limit permissions as demonstrated in the chart below:
Source: https://commons.wikimedia.org/wiki/File:Creative_Commons_Licenses.png
Source: https://commons.wikimedia.org/wiki/File:Creative_commons_license_spectrum.svg