Public domain documents are those that are not protected by copyright, given that the rights have expired, have been forfeited, or are inapplicable, i.e., those documents or pieces of information that are free for you to use without having to ask the author(s) for permission. In order for an item to be eligible to be an open educational resource it has to be openly licensed or in the public domain.
How to determine if a work is in public domain., e.g., publications dated before 1923 are automatically placed in public domain.
Teachers should clarify learners that there is a difference between public domain and open license (e.g., Creative Commons licenses) – both imply having free access to the documents or piece of information, but the scope and nature are different. In what concerns Public Domain, copyright ownership is waived and authors give away reproduction and distribution rights to them. As to Open License, copyright ownership is retained, but authors grant specific rights to the public.