Open Educational Resources (OER) are teaching, learning or research materials that are in the public domain or released with intellectual property licenses that facilitate the free use, adaptation and distribution of resources. United Nations - OER
Resources that are openly licensed benefit schools in a number of ways, but most notably they help to:
US Department of Education: Office of Educational Technology
The Five R's of Openness:
OERs include a wide range of materials: assessments, assignments, books, case studies, courses, journals, primary sources, reference materials, simulations, tutorials, tests, and textbooks.
This material is based on original writing by David Wiley, which was published freely under a Creative Commons Attribution 4.0 license at http://opencontent.org/definition