Peer-review is the key distinction between scholarly and non-scholarly sources.
In contrast to popular newspapers, magazines, websites, and books, scholarly sources are written by experts in a particular field and then reviewed (evaluated) by other experts in that field prior to publication.
Other clues that an article is scholarly:
The author is an expert. Most scholarly authors are affiliated with a college, university, or research institution. They hold relevant advanced degrees.
The article presents original research. This research can take many forms, but it often involves formal data analysis or theoretical discussion.
The article incorporates sophisticated, precise terminology. Experts writing for an expert audience typically use specialist language that will be unfamiliar to a reader outside the field.
The article includes a bibliography. Most scholarly articles include in-text citations, a reference list or works cited page. The bibliography helps the reader seek out the author’s sources and understand the larger “conversation” on a topic.