In the peer review process, a paper is submitted to a journal and evaluated by several reviewers. (Reviewers are often individuals with an impressive history of work in the area of interest, that is, the specific area that the article addresses). After critiquing the paper the reviewers submit their thoughts to the editor. Then, based on the commentaries from the reviewers, the editor decides whether to publish the paper, make suggestions for additional changes that could lead to publication, or reject the paper.
The primary purpose of peer review is to ensure that the papers published are valid and unbiased.