Peer-reviewed publications (sometimes called scholarly, academic, or refereed) have gone through a review process by experts in the field before being published. Library databases are good places to locate peer-reviewed articles, though not all sources found in those resources are peer-reviewed.
These strategies can help you determine if an article is peer-reviewed.
Learn more about the journal your article was published in:
Last resort: In many databases you can limit your search to only peer-reviewed articles. (This is not ideal, since it will remove some relevant items, such as peer-reviewed book articles.)