Open Educational Resources (OER) are classroom materials, like textbooks, that are created to be freely reused and modified. Most OER are either in the public domain or are licensed under a Creative Commons sharing license. OER are often created by educators and academics with grant funding.
"OER are 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." The William and Flora Hewlett Foundation