OER and Open Licenses
As generally defined, OERs are educational materials that are freely available and licensed to allow broad redistribution. To encourage this broad redistribution, OER creators often apply Creative Commons licenses to their materials which indicate such reuse is allowed. Creative Commons licenses allow creators of original works to waive some of the rights reserved under standard copyright.
The following chart visually explains the various permissions each Creative Commons licenses grants.

“CC License Poster” by Piotrek Chuchla used under CC BY 3.0 PL / Color coding added to original