Open Educational Resources are any resource used in learning, teaching, and research that are free to use and come with legal permissions for their use. Most importantly, OER are free to students.
The Consortium of Community College Open Educational Resources defines OER as "...educational materials that include permission for anyone to use, modify and share at no cost.”
According to The William and Flora Hewlett Foundation, OER is defined as: teaching, learning, and research resources that reside in the public domain or have been released under an intellectual property license that permits their free use and re-purposing by others. Open educational resources include full courses, course materials, modules, textbooks, streaming videos, tests, software, and any other tools, materials, or techniques used to support access to knowledge.