In academia, we keep referring to peer review as though it is something obvious, but it is not evident that there is a common definition. For journal publishers and universities, the most commonly used explanation is:
“…the process of someone reading, checking, and giving his or her opinion about something that has been written by another scientist or expert working in the same subject area” (from Cambridge Dictionary, web edition)
The review process should include comments from reviewers who are not on the editorial board and so can make objective decisions. Reviewers should focus on the academic quality of the work in question and check the methods used. Peer review does not involve language editing or copy editing, done to make the final article or book read well, but ensures that the research has been properly done according to discipline-specific and relevant research practices. Different types of peer review are suitable for different disciplines and research communities.
A trustworthy journal should clearly and publicly define what type of peer review it uses. It is also recommended that journals follow the guidelines provided by the Committee on Publication Ethics (COPE).
Definitions of the different types of peer review are also available.