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 either (1) in the public domain or (2) licensed in a manner that provides everyone with free and perpetual permission to engage in the 5R activities:
For more information, see David Wiley's discussion of openness
This material is adapted from Defining the "Open" in Open Content and Open Educational Resources, which was originally written by David Wiley and published freely under a Creative Commons Attribution 4.0 license at http://opencontent.org/definition/.
Unlike commercial textbooks and courseware products, OER are made available with open licenses. Licenses do not take the place of copyright -- the creator(s) still hold the rights to their work -- but open licenses allow the creator(s) to easily allow others the right to use their work under certain conditions. Creative Commons is the most common open license platform, and the most common of its licenses is the Attribution (CC-BY) license. This license simply requires the users to give credit to the creator(s), indicate how and/or if any changes were made, and provide a link to the license.
Professor X finds two different open textbooks and uses several chapters from each book. Professor X uses the chapters in a different order than in the original books, removes some of the chapters' sections, re-orders some of the sections, edits several sections for clarity and to include the most recent research, adds additional content from other OER sources, writes a new introduction to the material, and posts the finished product on the class website (and provides the University Library with a link to the material as well) for students to use in the class. Students can now access the content for free online, download it to their own devices, and/or print as many pages as desired. Which of the 5 R's did Professor X use?
Professor X used all 5 of the Rs!
Adapted from: Central Penn College, "Faculty Resources and Services: Open Educational Resources (OER)." https://guides.centralpenn.edu/facultyresources/OER/home