"Open educational resources (OER) are any resources available at little or no cost that can be used for teaching, learning, or research. The term can include textbooks, course readings, and other learning content; simulations, games, and other learning applications; syllabi, quizzes, and assessment tools; and virtually any other material that can be used for educational purposes."
From 7 Things You Should Know About Open Educational Resources
The terms "open content" and "open educational resources" describe any copyrightable work (traditionally excluding software, which is described by other terms like "open source") that is licensed in a manner that provides users with free and perpetual permission to engage in the 5R activities:
This material was created by David Wiley and published freely under a Creative Commons Attribution 4.0 license at http://opencontent.org/definition/.