According to UNESCO,
"Open Educational Resources are teaching, learning or research materials that are in the public domain or released with an intellectual property license that allows for free use, adaptation, and distribution."
Open Educational Resources (OER) can come in many forms, including curriculum maps, course materials, textbooks and supplemental materials, streaming videos, multimedia, assignments, and any other materials that have been designed for use in teaching and learning.
While there is a wealth of learning material available for free online, the open in OER integrates a community-minded model of free, where users can access, remix, add to, and legally distribute the material.
The Creative Commons has gathered a number of definitions of OER from different organizations.