Open Educational Resources (OER) are teaching, learning and research materials in any medium – digital or otherwise – that reside in the public domain or have been released under an open license that permits no-cost access, use, adaptation and redistribution by others with no or limited restrictions. UNESCO
Most open licensed materials use a Creative Commons license. For more information about Creative Commons licensing select the Copyright and Creative Commons tab on the left.
Open Educational Resources or OER allows adopters of OER materials to "Revise, Remix, Reuse, Re-distribute, and Retain" educational materials. These are known as the "5 R's of OER."