Peer review is a process designed to ensure the quality, more specifically the reliability and validity of material which is published in academic journals. It is absolutely central to the development of academic knowledge and provides a barrier to unfounded or poorly researched material finding its way into print. Articles submitted to academic journals are usually subject to a process of blind review by at least two other scholars who have been selected because of their expertise in the field covered by the article. People are not allowed to review their own work, and although they may be asked to review work by people they know, because articles are anonymised they should not know this when undertaking the review. There are flaws in this process but it remains considerably more robust than the free-for-all dissemination of claims that one finds on the internet and in other non-peer reviewed publications.
The process of peer review and its importance is described neatly in this short extract from the BBC series, Science Britannica presented by Professor Brian Cox, which was broadcast in 2013. Professor Cox is talking about the natural sciences, the process is the same for the social sciences and other disciplines. As he notes, although the process is not without its flaws, and its critics, it remains central