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. Open education resources include, full courses, course materials, modules, textbooks, streaming videos, tests, software, and any other tools, materials, or techniques used to support access to knoweldge." The William and Flora Hewlett Foundation
Open textbooks are on the rise, with more titles being introduced each year, many of them subject to peer review. To learn more about the open textbook publishing model, please see 7 Things You Should Know About Open Textbook Publishing.