OERs (Open Educational Resources).

"Open Educational Resources (OER) are teaching, learning and research materials in any medium – digital or otherwise – that reside in the public domain or have been released under an open license that permits no-cost access, use, adaptation and redistribution by others with no or limited restrictions." (UNESCO)

OER can be in the form of full courses, course materials, textbooks, curricula, syllabi, lecture notes, tests, assignments, videos, audio. etc.

Ideally, an Open Educational Resource (OER) allows the 5 R's. The CC0 License "allows owners of copyright- or database-protected content to waive those interests in their works and thereby place them as completely as possible in the public domain, so that others may freely build upon, enhance and reuse the works for any purposes without restriction under copyright or database law."