Peer-reviewed publishing is different from other types of publishing, like books, newspapers, and magazines.
The author is usually a professor or researcher and the article they submit to a journal goes through a rigorous process of review by other experts in their field of study before being published in a journal.
Sometimes, peer-reviewed is also called "scholarly" or "refereed." This distinction can be subtle. You can always ask a librarian for help determining if a source is peer-reviewed or not.