The Cochrane Collaboration (2021) has this definition.
A systematic review attempts to identify, appraise and synthesize all the empirical evidence that meets pre-specified eligibility criteria to answer a specific research question. Researchers conducting systematic reviews use explicit, systematic methods that are selected with a view aimed at minimizing bias, to produce more reliable findings to inform decision making.
The Cochrane Collaboration is highly-regarded in the Medical and Health areas. Specific methods used in Cochrane Reviews are discussed further on the same page and can be considered as principles for any systematic review.
Examples of Systematic Reviews can be found in the Cochrane Library (also indexed in databases such as Medline). The EPPI Research Centre covers Social Science subjects as well as Medicine and Health.
For details of what may be found in a Systematic Review, go to Key Elements of a Review.
