Open Education Resources refers to freely accessible content developed by people interested in fostering dialog and offering content to populations that might not otherwise have access or who might not be able to afford to pay for the content. Some OER resources are in the public domain while others have authors/owners who have used intellectual property licensing that permits their free use and re-purposing by others for specific purposes, such as education or creative works.
Common licensing symbols used by Creative Commons (one of the largest copyright clearance organizations for authors) include:
The least restrictive and most flexible license is "Attribution". When using an item with a license that requires attribution, you need to give credit to the author(s), and state where the item was obtained from; you may also be asked to follow other guidelines listed by the creator(s). When you use a "Share Alike" item, you can usually copy, distribute, display, perform, and modify the work, as long as you distribute any modified work on the same terms listed by the creator. If you want to distribute modified works under other terms, you must get permission first.
However, as an educational organization we need to be very careful of how items are used, as the "Non Commercial" use can be complicated if students have to purchase access to the content or course. Some (many?) authors are likely to view that as commercial use. For more information on Creative Commons and their licensing guidelines, please see their website.