OER stands for Open Educational Resources, and is a term that refers to any educational resources that are typically:
- Free to access online
- Low cost to get a print copy
- Licensed by the author/creator with rights that are less restrictive than copyright (i.e. all rights reserved). This license typically (though not always) includes the right of any user to copy (digitally) & print the text as well as the right to adapt it as desired for use in a course, as long as authorship is attributed and use is non-commercial.
Open Textbook is a specific type of OER that is designed to be a free or low cost substitute for a traditional textbook.