Systematic review
Short definition
A systematic review is a research synthesis that searches for, selects and appraises all relevant studies on a defined question, using an explicit, reproducible method set out before it begins.
In plain language
Unlike a narrative review, in which the author chooses which studies to cite, a systematic review defines in advance the question, the databases to search and the inclusion criteria, and assesses each study's risk of bias. It may or may not include a meta-analysis. It is one of the most highly valued forms of evidence, for example to find out whether virtual reality has been studied with good results for pre-operative anxiety.