Both Open Access and Creative Commons are online internet sites that provide access and use of materials without requiring permissions for the use of those materials usually through various types of licenses.
Creative Commons is a non-profit organization that enables creators to share their materials via a set of copyright licenses. There are standardized licenses that give the public permission to share and use works based on the rights the creator has chosen. Rights vary from some rights reserved. The user must read the accompanying license to know how the material can be used.
A work in the public domain is free for everyone to use without permission or paying royalties. The phrase ‘public domain’ is a copyright term referring to works that belong to the public. Works can be in the public domain for a variety of reasons: because the term of copyright protection has expired; because the work was not eligible for copyright in the first place; or because the copyright owner has given the copyright in the work to the public.
Note: These categories do not include traditional knowledge which exists outside of copyright and its exceptions.