Evidence synthesis is "the process of bringing together information from a range of sources and disciplines to inform debates and decisions on specific issues". A high-quality review should be "accurate, concise, and unbiased" (The Royal Society).
Compared to traditional (narrative) reviews, evidence synthesis "aims to reduce biases... [and] uses transparent and reproducible methods to exhaustively search for information on a topic and select studies based on well-defined predetermined criteria" (Eldermire & Young).
Evidence syntheses include systematic reviews, scoping reviews, meta-analyses, many other types of reviews. A common thread among these reviews is that they emphasize transparency, replicability, and exhaustive systematic searching.
Eldermire, E., & Young, S. (2022). World of Reviews. In M. J. Foster & S. T. Jewell (Eds.), Piecing Together Systematic Reviews and Other Evidence Syntheses (pp. 17-30). Find@UNC
The Royal Society. (2018). Evidence synthesis for policy: A statement of responsibilities. https://royalsociety.org/-/media/policy/projects/evidence-synthesis/evidence-synthesis-statement-principles.pdf