“Open access (OA) literature is digital, online, free of charge, and free of most copyright and licensing restrictions.”
[Open Access, Peter Suber, 2012]
"The realm of works that are unprotected by copyright or other intellectual property rights. With regard to copyright, works in the public domain include those never protected by copyright, those released to the public domain by their creators, and those for which copyright has expired.”
[Dictionary of Archives Terminology, Society of American Archivists]
All resources utilized in research should be evaluated for credibility. This includes: books, journal articles, websites, photographs, newspapers, videos, and more. Question everything.
Ask questions such as:
Who wrote it?
Who published it?
Where does the information come from? What sources does the resource cite?
Does the resource seem to have a bias?
How old is the resource?
Are there good reviews of the resource?
Will my audience accept this resources as reliable?