Peer-reviewed (also referred to as scholarly) articles appear in academic or professional journals. The term "peer-review" means that the content of each article is reviewed by a panel of experts for accuracy and authority prior to publication. Common components of a scholarly article include author credentials, literature review, methodology (if a research article), findings (if a research article), conclusions and a reference bibliography.
Magazine articles often do not include a reference bibliography, and in some cases the author and credentials are not listed. Without that type of information, it is difficult to verify the source. For most research projects, your professors will expect you to use strong, verifiable sources that have undergone peer-review prior to publishing.