Review of a study, service or recommendations by those with similar interests and expertise to the people who produced the study findings or recommendations.
Peer reviewers can include professional, patient and carer representatives.
The trouble is that peer review does not always (or even frequently) work very well. Many poor papers are published, and even papers published in top medical journals can have major flaws. Just because something is found in a peer-reviewed journal does not mean it is right, or good, or sensible.