Three Layers

There are three layers that make up the foundations of the Creative Commons Licenses:

Legal Code: The base layer, written so that terms and conditions of licenses are enforceable in court
Commons Deeds: The middle layer, summarized versions of the legal code meant to be easily interpreted by laymen
Metadata: Machine-readable versions of the licenses written in CC Rights Expression Language (CC REL) that allows software such as search engines to recognize the unique permissions of each license

Four Elements

There are four elements of a Creative Commons license, each has a stylized icon to easily indicate the permissions:

Attribution (BY) - you must always give attribution to the original creator, all licenses require this

ShareAlike (SA) - adapt and/or share work, adaptations must be licensed under the same license

NonCommercial (NC) - adapt and/or share work for noncommercial use

NoDerivatives (ND) - users cannot share adaptations of the work

These elements can be mixed and matched to create a total of six Creative Commons licenses

CC Licensing Versions

Since the Creative Commons licenses were first created, the legal code and deeds have been updated to reflect changes in copyright law, needs of users, and updates in technology. These changes to not alter the effect of the individual licenses, rather they serve to clarify and improve the existing licenses for users. The latest version of the CC license, Version 4.0, was published in 2013. More information about the recent version can be found on the Creative Commons Wiki.

Adaptations

One major difference between licenses is the ability to adapt and share the work. What is considered a true adaptation can depend on the nature of the work and applicable copyright law. For more information on adaptations, visit the Creative Commons FAQ page.

Commercial versus Non-Commercial Use

As with adaptations, another distinguishing feature among the licenses is the ability to use work for commercial purposes. Commercial use is loosely defined as one that is “not primarily intended for or directed towards commercial advantage or monetary compensation.” This is true whether the user is a nonprofit or private business, as the definition refers to the use and not the user. More information can be found on the Creative Commons Wiki.