"Open Educational Resources (OER) are teaching, learning, and research resources released under an open license that permits their free use and repurposing by others. OER can be full courses, course materials, lesson plans, open textbooks, learning objects, videos, games, tests, software, or any other tool, material, or technique that supports access to knowledge." - SPARC (Scholarly Publishing and Academic Resources Coalition)
The power of open educational resources comes from a set of permissions known as the "5 Rs of OER", which allows you to:
These permissions are usually granted by the copyright holder of a work by licensing it under a Creative Commons license.