Peer Review is a critical part of evaluating information. It is a process that scholarly journal editors use to ensure the articles they publish represent the best scholarship currently available. When an article is submitted to a peer reviewed journal, the editors send it to other scholars in the same field (the author's peers) to get their assessment of the quality of the scholarship, its relevance to the field, its appropriateness for the journal, etc. Most library databases will have a search feature that allows you to limit your results to peer reviewed or scholarly sources. Google Scholar does not have that feature.
This is a brief Alvin Sherman Library video explaining how to use Ulrichsweb to determine peer review status.