Peer review is the process by which most scientific journals evaluate articles submitted for publication. The "peer" part of peer review refers to the individuals who evaluate the articles for journals: they are researchers working in the same area as the author—thus, his or her peers.
The peer review process:
Reviewers evaluate manuscripts based upon their scientific validity—the literature cited, protocols followed, methods of analysis, and whether conclusions are substantiated by the data presented—as well as the originality and significance of their contribution to the body of scientific knowledge.
Peer review is not a guarantee
Articles that are peer-reviewed have been carefully evaluated by experts in the field, but this doesn't mean that everything in the peer-reviewed literature is proven. Results published in peer-reviewed articles may later be found to be unsound, or may simply be contradicted by new findings. The continual re-evaluation of previous research findings is one of the primary mechanisms by which scientific understanding is advanced.
However, information in the peer reviewed literature has undergone rigorous scrutiny by experts in the field, which is not necessarily true of non-peer reviewed publications. Scientific claims made in the non-peer reviewed literature should be considered with an extra degree of skepticism.
Once an article is published in a peer-reviewed journal, it is indexed in article databases like BIOSIS Previews, Web of Science, PubMed, or Scopus. The same journal can be indexed in more than one database.
To locate peer-reviewed articles, search by topic, author or other fields in an appropriate database. See Bio 1B Library Guide: Searching for articles.
Look at the journal in which the article was published:
If you are still in doubt, consult a reference librarian.