Peer-review is the process journal publishers use to choose high-quality research articles for publication. The journal editors ask a group of experts in a field to read articles that scientists have submitted to the journal. The experts read the articles, make comments or suggestions for edits and then make a final recommendation about whether they think the article is worthy of publication. If an article receives enough approval from the experts then it is published in the journal and qualifies as peer-reviewed.
Some journals use peer-review for all articles. Others use it only for some articles. Remember that even if a journal’s articles are entirely peer-reviewed there is content like book reviews, editorials and letters to the editor that are not peer-reviewed.
Use the peer-review limiter in databases to find articles. Use the Ulrich's Periodical's database to determine whether a publication is peer-reviewed.