Open Educational Resources (OER) are teaching, learning, and research resources that are free of cost and access barriers, and which also carry legal permission for open use. They can include things like open textbooks, audio and video material, test questions, simulations, labs, slides, and anything else you might use in the course of teaching. Open Educational Resources must either be in the public domain or licensed in a manner that provides users with free and perpetual permission to engage in the 5R activities described below.
This video explains the basics of open education and explains why it is so important:
Citation: Why Open Education Matters by Degreed