"Open Educational Resources" (OERs) are any type of educational materials that are in the public domain or introduced with an open license. The nature of these open materials means that anyone can legally and freely copy, use, adapt and re-share them. OERs range from textbooks to curricula, syllabi, lecture notes, assignments, tests, projects, audio, video and animation" (UNESCO).
Traditionally published textbooks and educational materials are subject to copyright restrictions, which do not allow them to be modified or reused in other contexts. With OER, students and instructors can re-use and re-purpose materials not just during the class, but in the future as well.