Peer-reviewed:
noun
a process by which something proposed (as for research or publication) is evaluated by a group of experts in the appropriate field.
https://www.merriam-webster.com/dictionary/peer/review
Why is peer review needed?
Scholarly articles are written by experts in a field. The article is then reviewed by the writer's peers. Typically, these peers are also experts in the related field. Articles need to be reviewed before publication as a type of quality control.
Basic Example:
Dr. H. Jones is an insect expert. One day Dr. Jones finds an ant, captures it, and studies the specimen. This ant appears different than other specimens. Dr. Jones writes a paper on the ant. Jones uses reference material to explain the differences and similarities of the ant and other species. The reference material also supports Jones's theory that the ant may be a new species. Photos and diagrams of the ant are included.
Dr. Jones sends the completed paper to be reviewed by other insect experts. The experts closely examine the information and conclude that it would be a beneficial addition to an academic journal focusing on insects.