Peer-reviewed journals require that articles are read and evaluated by experts in the field before they are accepted for publication. Although most scholarly articles are refereed or peer-reviewed, some are not.
If your professor asks you to provide evidence to support your claims using peer-reviewed journal articles, be sure to double check that the journals you are citing are recognized as peer-reviewed.
If you aren't sure, investigate further by visiting the journal's website and reviewing information about the journal, or their submission guidelines.