OER stands for Open Educational Resources. They consist of teaching and learning materials available online and distributed free of charge. OER includes textbooks, exercises, course readings, homework sets, quizzes, or any other materials that can be used by faculty and students for education. In most cases, these materials have been vetted and reviewed by other educators for clarity and accuracy.
OER are issued under specific copyright licenses that allow you and your students to use them freely. Some of these licenses require that the material be used in its original form while others allow for modification of the materials to suit your particular audience or students.
Textbook Cost Zero, also known as a "Z" course is a course where the associated costs of materials for students is $0. Obviously, a course exclusively using OER already has a materials cost of $0. However, you can also achieve this by using a combination of resources already purchased by the library or using primary sources/documents freely available online. Think of a course packet where all the readings are actually links to articles from the Library's databases and/or links to items held in the public trust or free from copyright restrictions. The final cost of materials to the student would be $0.
Here is a great FAQ about textbook cost $0 from Wayde Oshiro at the Leeward Community College Library.
In creating OER, producers subscribe to the framework of the 5Rs