Peer review, or scientific refereeing, is the basis of the academic process. It’s a rigorous evaluation that aims to ensure only work which advances knowledge is published in a scientific journal. Scientists must be able to trust this system: if they see that something is peer reviewed, it should be a hallmark of quality.
When the editor of scientific journal receives a manuscript, they ask other another scientist – a specialist in their field – to review it. The referee is required to advise the editor whether the manuscript should be published and to give feedback to the authors.
The system is not flawless. There have been instances of fraud and manipulation due to refereeing, but these are – we hope – isolated cases.