OER include textbooks, topic-specific learning tools for coursework, syllabi and lesson plans, videos, assignments, tests, and even whole courses created by other instructors and shared openly for others to modify and reuse in their own teaching.
They are published under open licenses that describe how materials can be used, reused, adapted, and shared in your own courses.
When using OER under an open license for your own purposes, there are five aspects of use that make it so flexible. They are the Five Rs.
This material is an adaptation of 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/.