Public Domain, Wikimedia Commons
Open Educational Resources (OERs) are teaching, learning, and research resources released under a license that permits their free use and repurposing by others. OERs can be full courses, software, or any other tool, material, or technique that supports access to knowledge.
Open Educational Resources are broadly considered to meet the "5Rs Framework," meaning that users are free to:
OERs are any type of educational material that’s freely available for teachers and students to use, adapt, share, and reuse. They are not the same as public domain materials. Most of the time, someone still owns the copyright.