Peer Review is a process that articles may undergo to be published in a journal. It can be a lengthy process, taking months or years for an article to go from submission to publication.
Once an article is submitted, an editor reviews it to determine if it fits in the topic scope with the journal. If it does, the editor passes it on to a team of reviewers. These reviewers are experts in the field of study the article is based in. They will read the article and determine if it meets a selection of criteria, including but not limited to authority, relevancy, etc. Many times reviewers make comments on the article and expect revisions to be made before the article is published. This revision process could occur multiple times before the reviewers feel the article is of a high enough quality to publish.