Libraries subscribe to various types of periodicals, such as scholarly (some of which may be peer-reviewed, blind peer-reviewed, editorial review) popular, or trade publications. Choosing which to use depends on your topic, the type of writing you are doing, your assignment, and the sources your professor wants you to use. Many databases offer the option to limit to "Peer Reviewed". If you're not sure if a journal is considered peer-reviewed, check Ulrich's by looking up the title of the journal.
What is a peer-reviewed journal?
A scholarly/academic journal is peer-reviewed when manuscripts are sent to experts, sometimes anonymously (blind peer-reviewed), in the related field. They make recommendations to editor for publication, rejection or revision. These journals are generally thought to be of the highest quality.