"Open Educational Resources (OER) are teaching, learning, and research materials that are either (a) in the public domain or (b) licensed in a manner that provides everyone with free and perpetual permission to engage in the 5R activities:
Retain – make, own, and control a copy of the resource
Reuse – use your original, revised, or remixed copy of the resource publicly
Revise – edit, adapt, and modify your copy of the resource
Remix – combine your original or revised copy of the resource with other existing material to create something new
Redistribute – share copies of your original, revised, or remixed copy of the resource with others."
Source: Creative Commons (click to read more)