OER is the frequently used acronym for Open Educational Resources.
Open Educational Resources (OER) are defined as instructional materials that are fully accessible and 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
This is the DOERS3 definition of OER, adapted from the Hewlett Foundation definition of OER. It is reused here thanks to a Creative Commons-Attribution license.