Open Educational Resources (OER) are teaching, learning and research materials in any medium – digital or otherwise – that reside in the public domain or have been released under an open license that permits no-cost access, use, adaptation and redistribution by others with no or limited restrictions.
Source: UNESCO - Open Educational Resources
When OER textbooks are used for course readings they have the potential to save students money.
OER have been created by other educators and shared with the purpose of helping other educators. They include a variety of educational products like lesson plans, assignments, exams, and other in-class activities.
OER are by definition free and available for reproduction, they can be shared and made available to students quickly and without worry about copyright violations.
Since OER are usually offered with Creative Commons licenses they can be used and reused multiple times, depending on the type of open use licenses they come under.
Educators who have created impactful teaching content can share it with other educators and students all over the world. This helps improve the reach of the best educators and helps students learn from the best.