Q: What is ZTC?
A. Zero textbook cost means that students do not incur any costs for purchasing course material. However, zero-cost to the students does not guarantee zero cost to the institution, ie. subscription databases, library equipment loans. To create a course that is at zero-cost to students, course instructors can use many platforms including Open Educational Resources; Open Access, Creative Commons, and public domain materials; along with resources owned or licensed by the Library.
Q. What is OER?
A. OER stands for Open Educational Resources. "Open Educational Resources are teaching and learning materials that you may freely use and reuse, without charge. OER often have a Creative Commons or GNU license that state specifically how the material may be used, reused, adapted, and shared” (OER Commons). OER materials can include textbooks, test materials, instructional videos, and other learning materials and tools.
OER might be similar to what you are currently doing. If you have ever used a worksheet that another instructor created, that's the basic concept of OER. Fundamentally, the only difference between OER and the worksheet you got from a colleague (or vice versa) is that the open license gives you and others formal permission to use, adapt and share it.
Source: Adapted from Skyline College ZTC FAQ