Open Access (OA) refers to removing barriers such as "paywalls". Open Access initiatives seek to make research articles and other works easy to find and read, for free. It does not address copyright, but rather the methods of funding and accessing the research or other works.

Open Educational Resources (OER) are works that copyright owners have "opened" by adding a Creative Commons or other License that removes some copyright restrictions.  The ideal is to allow others to "retain, reuse, revise, remix, and redistribute" without needing to ask for permission, as long as the work is attributed to the copyright owner, giving credit where it is due.