Many professors will require that students only use “peer-reviewed” articles in their bibliographies. This causes a problem when students are unsure what peer reviewing actually means.
In understandable terms, peer reviewing is about the process that a resource undergoes before it is published.
This is best explained in a scenario: let’s pretend I’m a researcher and I’ve written an article. When I submit this article to a journal for publication, it is reviewed anonymously by different experts in my field: I don’t know who the reviewers are, and they don’t know my name (This system is called “double blind,” meaning that bias can’t affect how my article is reviewed). I then receive my article back from the reviewers, make any corrections or changes they suggest, and re-submit it to the journal for publication.
Peer reviewed journals, then, are often considered more credible than open-access or non-peer reviewed journals, since experts have reviewed the content/methodology/conclusions, et cetera, and still said it should be published.