What sets open resources apart is the "open" license, which enables two key features:
Open licenses do not replace copyright; they work with copyright law to change the default setting from "All Rights Reserved" to "Some Rights Reserved." Under U.S. law, copyright is the exclusive right to dictate how users copy, distribute and adapt a work. By default, all of those rights are reserved by the author, and anyone who wants to use it needs to get permission from the author in the form of a license. Open licenses are a particular kind of license that enable authors to grant blanket permissions to everyone, which makes it much easier for people to legally use the material in the ways the license allows.
Adapted from Open Education Primer by SPARC Open Education Leadership Program licensed under a Creative Commons Attribution 4.0 International License. Available at sparcopen.org/leadership-program
Works that are no longer protected by copyright are considered part of the public domain. Items in the public domain can be reused freely for any purpose by anyone, without giving attribution to the author or creator (though standard citation procedures apply).
Public domain works in the U.S. include works whose creator died 70 years prior, works published before 1924, or works dedicated to the public domain by their rights-holder. The Creative Commons organization created a legal tool called CC 0 to help creators dedicate their work to the public domain by releasing all rights to it.
Adapted from The OER Starter Kit by Abbey K. Elder is licensed under a Creative Commons Attribution 4.0 International License. Available https://iastate.pressbooks.pub/oerstarterkit/chapter/copyright/