One definition is: “Open Educational Resources are teaching and learning materials that you may freely use and reuse, without charge. OER often have a Creative Commons or GNU license that state specifically how the material may be used, reused, adapted, and shared.“
(from OER Commons https://www.oercommons.org/about#about-open-educational-resources)
In short, OER can be defined as resources that are:
- Freely accessible (open!!)
- Open licensed (there are various licenses)
- Resources for learning, teaching, research, etc.
- Can be resources such as text, audio, video, and images (and are typically digital).
What are OER and how do they differ from traditional textbooks? BCcampus has a good write up about this as below that is worth checking if interested.