An Open Education Resource (OER) is a teaching resource that can be used and reused freely for educational purposes because the author(s) have freely released the work to the public for that purpose - usually using one of the six types of a Creative Commons licence.
"The 5 Rs".
In order for a resource to qualify as an Open Educational Resource, users should be able to
Open Access Educational Resources come in many forms, from images and media files that can be used in teaching to presentations, lecture notes, assignments, and free textbooks. This guide provides a list of high quality sources of Open Access Educational Resources organized by format. All of these OERs can be used freely for non-commercial purposes usually only with the condition that you cite or attribute the work.
Video from teachonline.ca by http://contactnorth.ca is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
SUNY (State Universities of New York) has developed a search tool that currently searches content from 98 different sources and contains over 350,000 records (as of January 2020).