Your instructor may want you to use "peer reviewed" articles as sources for your paper. Or you may be asked to find "academic," "scholarly," or "refereed" articles. What do these terms mean?
Let's start with the terms academic and scholarly, which are synonyms. An academic or scholarly journal is one intended for a specialized or expert audience. Journals like this exist in the sciences, social sciences, and humanities. Examples include Nature, Journal of Sociology, and Journal of American Studies. Scholarly/academic journals exist to help scholars communicate their latest research and ideas to each other; they are written "by experts for experts." Magazines like Time or Scientific American, newspapers, (most) books, government documents, and websites are not peer-reviewed, though they may be thoroughly edited and fact-checked.
Most scholarly/academic journals are peer reviewed; another synonym for peer reviewed is refereed. Before an article is published in a peer-reviewed journal, it's evaluated for quality and significance by several specialists in the same field, who are "peers" of the author. Many times this is a "blind review" where the reviewers do not know who the author is and vice-versa. Reviewers make comments and edits of the article and send those back to author before publication. The article may go through several revisions like this before it finally reaches publication.
How do you find peer-reviewed articles? The easiest way to know if an article is peer-reviewed is to select the "peer-reviewed" (scholarly, refereed, etc) limit in an article database.
How can you tell if an article is peer-reviewed? A couple clues will alert you:
As you become more familiar with an academic discipline, you will learn the peer-reviewed journals in that field.