Peer reviewed (or refereed) journals have been reviewed by a panel of subject experts, a researcher's "peers." Peer reviewers scrutinize articles for significance, relevance, sound research design, accurate presentation, and clarity before they are accepted for publication.
Many databases allow searches to be limited to peer-reviewed journals. Look for a limit box to check for peer-reviewed or refereed. You can also use Ulrich's International Periodical Directory to check a journal's peer-reviewed status. Look for a referee jersey icon to indicate that a journal is peer-reviewed.