All Open Educational Resources (OER) are Open Access (OA). But not all OA are OER. OA resources can be reused and shared, but OER can be adapted and changed to meet a broader need. This is possible due to the type of creative commons license used which allows for the 5 Rs to take place.
OER: Open Educational Resources are openly licensed educational materials which can be shared, reused, and remixed to create new educational content.
Open Access: Open Access is free, permanent, full-text access to scholarly and scientific materials. Open access allows for sharing content with no license requirements. Open access does not allow for the alteration or reuse of materials.
For more information on Creative Commons Licenses please see the library's guide on copyright.