In this TED talk, Prof. David Wiley at BYU talks about what open education is, and why you should care. The video is about 15 minutes long, but the first minute or so will introduce you to the concept of OER and how it works.
Open educational resources are information assets that are freely accessible to use and openly licensed. They can include textbooks, media resources, and other digital assets meant to enhance teaching, learning, and assessment.
"Open-access (OA) literature is digital, online, free of charge, and free of most copyright and licensing restrictions. What makes it possible is the internet and the consent of the author or copyright-holder." -- Peter Suber, A Very Brief Introduction to Open Access