"ZTC" and "OER" are not equivalent terms.
Here is one of the most often cited definitions of OER:
William and Flora Hewlett Foundation’s definition: “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." "Open educational resources include full courses, course materials, modules, textbooks, streaming videos, tests, software, and any other tools, materials, or techniques used to support access to knowledge.”
While the definition of ZTC, as we use it in California, comes from the language of the legsilation that created the use of this designation on our online class schedules.
ZTC Checklist includes: