Open Educational Resources (OER) are teaching, learning, and research resources that are free of cost and access barriers and also carry legal permission for open use. They include a multitude of formats, including textbooks, full courses, modules, videos, labs, assignments, and assessments.
What makes them "Open"?
OER are licensed in such a way that enables adopters to utilize the 5 Rs:
Retain a copy of the content
Reuse the content in a range of ways
Revise the content as needed
Remix original or revised content with other material
Redistribute the original, revisions, and remixes with others