Some definitions:
"technology-enabled, open provision of educational resources for consultation, use and adaptation by a community of users for non-commercial purposes" (UNESCO, 2002)
"teaching, learning, and research resources that reside in the public domain or have been released under an intellectual property license that permits their free use of re-purposing by others" (Atkins, Brown, & Hammond, 2007)
In other words, OER are educational resources that have been released under less-restrictive licenses than traditionally published material.
OER can take many forms, such as:
Atkins, D.E., Brown, J.S., & Hammond, A.L. (2007). A Review of the Open Educational Resources (OER) Movement: Achievements, Challenges, and New Opportunities. http://www.hewlett.org/uploads/files/ReviewoftheOERMovement.pdf
UNESCO. (2002). UNESCO promotes new initiative for free educational resources on the Internet. United Nations Educational, Scientific and Cultural Organization Education News. http://www.unesco.org/education/newsen/080702freeeduress.shtml
OER offer many of advantages for both faculty and students, but they also have some challenges the community still needs to tackle: