Open Educational Resources (OER) are "teaching, learning, and research resources that reside in the public domain or have been released under an intellectual property license that permits their free use and re-purposing by others."
OER allow users to:
Open Textbooks have been released with an open license (usually a Creative Commons license) which allows them to be copied, shared and revised.
OER Repositories contain more than just open textbooks. They also have other digital learning materials such as: