"We’ve just added the seal you see at right to Creative Commons licenses that qualify as Free Culture Licenses according to the Definition of Free Cultural Works — Attribution and Attribution-ShareAlike. Public domain is not a license, but is an acceptable copyright status for free cultural works according to the Definition.

One obvious way to think of the definition is as an application of the principles of free software to content. These demand the freedom to modify without any discrimination against uses or users, which means that Creative Commons licenses containing the NonCommercial or NoDerivatives terms do not qualify..."