Open Educational Resources (OER) are teaching, learning and research materials in any medium that reside in the public domain or have been released under an open license that permits no-cost access, use, adaptation and redistribution by others.
Definition from Creative Commons. Other definitions can be found here: https://wiki.creativecommons.org/wiki/What_is_OER%3F
You don't have to go full OER
OER are great! So are library resources and traditional textbooks and materials! You can use them in combination, though you probably can't adapt paid resources. Check out this sample of library resources with potential for your classes. Looking for something? Contact your librarian!
Creative Commons (CC)
Many open educational resources are made available under the terms of Creative Commons licenses. Most, but not all, Creative Commons licenses are suitable for Open Education Resources. Licenses that do not allow users to create derivative works are not fully open.
Creative Commons (CC) is a non-profit organization dedicated to expanding access to creative works. Creative Commons makes their licenses freely available to the public. These licenses allow creators to clearly communicate which rights they wish to retain and which rights they waive for the benefit of others.
Creative Commons is a great resource for creators and users of content. All Creative Commons licenses require users to attribute works to their author. Learn more about attribution under Creative Commons licenses here.
"Creative Commons." Wikipedia: The Free Encyclopedia. Wikimedia Foundation, Inc., 9 May 2018. en.wikipedia.org/wiki/Creative_Commons. Accessed 14 May 2018.
Creative Commons. "What we do: What is Creative Commons?" creativecommons.org/about. Accessed 14 May 2018.