Peer-review is the system used to assess the quality of a manuscript before it is published. Independent researchers in the relevant research area assess submitted manuscripts for originality, validity and significance to help editors determine whether the manuscript should be published in their journal. You can read more about the peer-review process here.
Journal of Patient-Reported Outcomes operates a double-blind peer-review system, where the reviewers do not know the names or affiliations of the authors and the reviewer reports provided to the authors are anonymous.
The benefit of double-blind peer review is that it allows reviewers to judge the manuscript based on content alone, and they are not unconsciously biased by knowledge of who the authors are.