Open access (OA) is a set of principles and a range of practices through which research outputs are distributed online, free of cost or other access barriers. (Wikipedia, https://en.wikipedia.org/wiki/Open_access)
Open access (OA) focuses on those articles that are peer-reviewed literature and research studies Typically we think of OA as research studies and journal articles but OA may also include books, conference papers, individual book chapters and theses.
Open access (OA) access means free to use but not to retain, reuse, revise, remix, redistribute.
The list is ever changing and every growing as more authors are willing to allow access to their books.
"Open Access Explained" created by Piled Higher and Deeper (PHD) Comics under CC BY
"Open educational resources" describe any copyrightable work (traditionally excluding software, which is described by other terms like "open source") that is licensed in a manner that provides users with free and perpetual permission to engage in the 5R activities:
"What are OER with ncLibraries?" created by ncLibraries under CC BY
While it is tempting to believe that Open Access works are somehow more reliable than OER, it is not the case.
Open Access was designed to enable the sharing of research documents and academic journals online. It has been extended to also include textbooks.
If you are an educator looking for free alternatives to the expensive textbooks that your students may be using and you want to use them as they are, OA may be for you.
OER was designed to provide students and educators free access to educational materials appropriate for use in curriculum. It has expanded into resources that are free to use both in education and outside of education. OER will always be free. If it is NOT free, it is NOT OER.
If you are an educator looking for access to free materials for your students which may be more flexible for your classroom and, OER may be for you.
Please follow the copyrights attached to any materials you may use, these are Open Access or OER materials and are not public domain (free to use for any reason).