OERs (Open Educational Resources) are not just books. They can be any educational material for teaching, learning, and research that are “intentionally created and licensed at low cost/no cost for the end user to own, share, and in most cases, modify” (Creating Killer OERs).
Source: Knockemus, M. and Stafford, R. Creating Killer OERs. SC Technical College System October TLT. Webinar
OERs: Not Just Books