Peer-reviewed articles are also known as "scholarly" or "refereed" articles. Before being accepted for publication in a journal, they have been reviewed by a panel of experts in that field or on that topic. Peer-reviewed articles are the best available.
A search in Academic Search Complete and other select research databases can be limited to peer-reviewed journal articles by checking off the "Scholarly (Peer Reviewed) Journals" box under "Limit your results."
Another way to determine if an article is peer-reviewed is by checking the journal, not article, title in Ulrich's International Periodical Directory. Enter the journal title and if a referee shirt is shown in the listing, it is refereed or peer-reviewed.