When looking at the CC licensing in a document, you may find that it refers to ported or unported license.

Unported licenses are licenses that are not ported to any specific jurisdiction. They do not mention any particular jurisdiction’s laws or statutes or contain any sort of choice-of-law provision. In theory, the unported version will "work" under all of the various legal systems. Because of subtle differences in both legal systems, and how various countries interpret the various WIPO treaties on copyright, the unported version may include/exclude clauses that are either not legally binding, or legally meaningless, in any specific jurisdiction – and thus, some aspects of the license may not align perfectly to a particular jurisdiction's laws.

Creative Commons started the international porting process to create localized versions of the main 'unported' licenses. Creative Commons is working to "port" the core Creative Commons Licenses to different copyright legislations around the world. The porting process involves both linguistically translating the licenses and legally adapting them to particular jurisdictions. These licenses are designed to have the same effect anywhere in the world while at the same time following the legal conventions of particular jurisdictions, so that they can be more easily understood and used by the local community. Thus, usage of these jurisdiction-specific licenses have started replacing in some occasions the unported licenses.

Local CC teams promote the ported licenses in their respective jurisdictions but the unported licenses still enjoy widespread use, if not for any other reason, then because they have been traditionally used in many high traffic websites, and are still a common choice for users in jurisdictions with no ported versions.

Sources

CC Monitor - http://monitor.creativecommons.org/Unported

Creative Commons International - http://creativecommons.org/international

You can find out more about the licensing porting process at http://creativecommons.org/international