A systematic review is a critical assessment and evaluation of primary research studies. 
In systematic reviews, insignificant, unsound, or redundant literature is separated from the salient and critical studies. Systematic reviews also address random and systematic errors of bias, assess consistencies among many studies, and explain data inconsistencies and conflicts.
Additionally, because systematic reviews synthesize data from multiple research studies, they enable medical clinicians to keep abreast of large volumes of medical research.
Systematic reviews are considered the gold standard source of information for Evidence-Based Medicine.