A peer-reviewed publication is an information source that has been reviewed prior to publication by experts in the field. The most common peer-reviewed publications are academic (aka scholarly) journals and conference proceedings. Other types of information sources that may be peer-reviewed include handbooks, encyclopedias, standards, and technical reports.
Examples of information sources that are not peer-reviewed include preprints (unpublished articles), professional magazines, popular magazines, Wikipedia articles, and blogs.
The peer review process begins when an author sends a draft article (aka manuscript) to a journal. The editor of the journal then sends the manuscript to one or more referees who are experts in the field. The referees read the article and return it to the editor with comments or suggestions on how the article could be improved. The editor will then share the referees' comments with the author and ask them to revise and resubmit their article. This process continues until the editor and referees are satisfied that the article is fit for publication.
If you'd like to know more about the peer review process, watch the short video below produce by the American Chemical Society.
