In order to fully understand OER, you need to understand a little bit about copyright.
"Copyright protection subsists, in accordance with this title, in original works of authorship fixed in any tangible medium of expression, now known or later developed, from which they can be perceived, reproduced, or otherwise communicated, either directly or with the aid of a machine or device" (17 U.S.C. § 102).
Copyright refers to a creator's exclusive right to duplicate, distribute, tweak, remix, or publicly perform or display their works. Copyright protects fixed, original, and creative works. Further, copyright protection exists whether or not there is a notice included with the work--it is presumed the moment a work is created and fixed in a tangible form.
There are many excellent resources that give an overview of the essentials of copyright.
Provided by the University of Texas Libraries, the The Copyright Crash Course (CCC) was originally created with faculty in mind, but can be used by anyone who is interested in understanding and managing their copyrights. It contains a wealth of information and examples.
Copyright Law and Resources from the U.S. Copyright Office
Fair use offers an exception to the exclusive copyright protections granted to a creator. Fair use enables limited use of works--typically for purposes of criticism, comment, reporting, teaching, or research--without obtaining permission from the creator or copyright holder. There isn't a definite rule as to whether a use of a work is "fair," but rather each of the following four factors must be considered:
The Four Factors of Fair Use
Purpose and character of the use
Nature of the copyrighted work
Amount and substantiality of the portion used in relation to the copyrighted work as a whole
Contrary to popular opinion, being an educator doesn't exempt you from copyright restrictions. However, it's true that there are some exceptions and limitations under copyright law for using other people’s works for educational purposes.
Additional resource with copyright situations specific to education and educators.
And what does this have to do with OER???
All of these copyright rules and exceptions are in place on any created work, but creators have the ability to choose what is done with the works they create. And that's where OER comes in.
By applying an open license such as a Creative Commons license (more about that on the next page), the creator indicates that they want others to be able to use their work freely and openly. They can also designated how they would like that to be done.