A literature review is both a summary and analysis of the relevant, available research and non research on a specific topic. Knowledge gaps, or gaps in the research could not be identified without a review!
A review summarizes and critiques a body of literature and draws conclusions about the topic, it is not an annotated bibliography and it does not present new data but the findings from previous research.
Provides the reader with comprehensive background for understanding current knowledge of a topic.
Inspires research ideas by identifying gaps or inconsistencies and helps avoid research duplication.