Peer review is a process used when publishing documents where the work is reviewed by the author's peer group (someone in their field). It is a way of checking and reviewing a person's work. It is often used by scientists, scholars, medical professionals, engineers, and in some aspects of government.
For example, scientists report new discoveries through a peer review process. This means that they ask other knowledgeable scientists (peers) to review their report, and check for any problems. The problems must be fixed before the report is released to other scientists. This process helps to maintain the trustworthiness of scientific discoveries.