Articles published in peer-reviewed or refereed journals have been through a formal approval process. An editor and one or more subject specialists review the article before it is accepted for publication. This process is intended to ensure that the article is accurate, well-researched, and contributes to the body of knowledge in the field.
Primo Search and some Journal Databases include an option to limit your search to scholarly or peer-reviewed articles, and some other databases include this information as part of an article record. While this is an indication that the article could be peer-reviewed, the definitive way to find out is to use Ulrichsweb Global Periodicals Directory. You can access this database from the Library's list of U-databases.