Researchers consult and use information to inform and build upon their research, just as policy-makers might use this information to guide decisions.
This process exists to ensure that high quality information gets published.
Not all content in a peer-reviewed journal has been through the peer-review process.
It turns out that some peer-reviewed journals contain a mix of content including editorials, letters to the editor, opinions, book reviews, and commentary (in addition to articles), none of which is peer-reviewed. It's only the articles that are peer-reviewed, because they contain research results.
Important to note: Information that comes from peer-reviewed sources is not always accurate and reliable. Researchers and scholars make mistakes and - occasionally - deliberately mislead. All we can really say for sure is that peer-reviewed sources are less likely to be flawed and inaccurate, compared to other types of sources.
What types of sources are considered to be peer-reviewed?
1. Scholarly journal articles.
2. Some scholarly books are either editorially reviewed or peer-reviewed or both.
What is the peer-review process?
When researchers conduct studies, they write up the results of those studies in the form of a journal article. Then, they submit the article to a journal in the hopes that the journal will publish it.
The editor of the journal (this is the person in charge of all the content published in the journal) will receive the submitted article and then identify a few experts who are peers of the author - that is, other experts working in the same discipline as the author. The editor will send the submitted article to those peers.
The peers will review the article to determine whether the authors' research methods seem to be valid and their conclusions make sense. They might also look at the importance and utility of the research, as well as the quality of the authors' writing. If the peers like it, they'll recommend that the article get published. If they don't like it, they'll let the editor know that they think the article should be revised and reviewed again, or rejected and not published.
Any journal that has this vetting process in place is called a peer-reviewed journal.
"Peer Review is defined as “a process of subjecting an author’s scholarly work, research or ideas to the scrutiny of others who are experts in the same field” (1). Peer review is intended to serve two primary purposes. Firstly, it acts as a filter to ensure that only high quality research is published, especially in reputable journals, by determining the validity, significance and originality of the study. Secondly, peer review is intended to improve the quality of manuscripts that are deemed suitable for publication. Peer reviewers provide suggestions to authors on how to improve the quality of their manuscripts, and also identify any errors that need correcting before publication."
Kelly, J., Sadeghieh, T., & Adeli, K. (2014). Peer Review in Scientific Publications: Benefits, Critiques, & A Survival Guide. EJIFCC, 25(3), 227–243.