What is OER?
The term “Open Educational Resources” (OERs) was created at UNESCO’s 2002 Forum on the Impact of Open Courseware for Higher Education in Developing Countries to describe a new global phenomenon of openly sharing educational resources in 2002. This campaign to make freely adaptable content known as OER widely available has gathered momentum. Subsequently, a global community of OER producers has emerged and institutions are incorporating these resources into their teaching and learning strategies. - United Nations Educational, Scientific and Cultural Organization.
Nutshell version: OER = educational resources that are free to use