A scholarly publication is considered "peer reviewed" (or "refereed") if it is examined by other scholars in the same field ("peers") before getting published. It usually works like this:

• A scholar writes an article about some research they did, and what they found. They then submit their manuscript to the editor of a scholarly journal to be considered for publication.
• If the journal editor thinks the article would be interesting to their journal's readers, they can submit it to a jury of peer reviewers (usually at least two), who are other scholars recruited by the journal to do this work.
• The peer reviewers and the author are anonymous to each other (referred to as "double-blind"). The reviewers read the article and make sure it was written with appropriate scholarly rigor and that it conforms to the standards of their field. For example, ensuring a large enough sample size was used for a social experiment, or that all of the relevant literature was consulted and conclusions are properly supported.
• The reviewers usually make extensive comments and might question some portions of the article to make sure the author can support their arguments. Then the vote on whether to accept the article for publication, send it back to the author for revisions ("revise and resubmit"), or reject it.
• Manuscripts can go back and forth between the reviewers, the editor, and the author multiple times before a decision is reached. Usually the journal's editor makes the final decision on publication based on the votes of the peer reviewers.  

WHY GO TO ALL THIS TROUBLE? Although not a perfect system by any means, peer review ensures that there is some level of consensus among other scholars before an article is published. Readers of peer reviewed journals know that articles were not chosen for sensationalism, but because of the significance and validity of the work.   

Books and Book Chapters

A book would be considered scholarly if it shares the same traits as scholarly journal articles in the above table. Often scholarly books come from what are called "university presses." University presses are usually non-profit publishing operations that prioritize publishing academic research that is academically significant rather than potentially profitable. Examples of university presses include Oxford University Press, Harvard University Press, and our very own Penn State University Press. University presses usually have the word "university" in the name. If you are unsure about whether a publisher is a university press, look them up online and see if they are associated with an academic institution. Generally speaking, books published by university presses are understood to have some level of peer review.

Book chapters are section of a book, sometimes referred to as an "edited volume" or an "anthology." These books will have an editor, who selects scholars to write individual chapters in the book. Edited volumes can come from university presses or commercial publishers who specialize in scholarly works, e.g., Elsevier, Springer, Taylor & Francis. They are usually considered scholarly, but not necessarily peer-reviewed.

The other stuff: "Grey Literature"

Publications that don't fit neatly into traditional categories are sometimes called "grey literature." Grey literature is generally considered scholarly in terms of authorship, audience, and intent. However, it is not peer reviewed. Examples of grey literature include:

• Reports from scholarly organizations
• Policy papers from "think tanks"
• Conference papers and presentations (often published in something called "conference proceedings")
• Government-commissioned reports
• Theses and dissertations  

If you are ever not sure, just ASK A LIBRARIAN!