"A literature review is an objective, thorough summary and critical analysis of the relevant available research and non-research literature on the topic being studied (Hart, 1998). (https://www.ncbi.nlm.nih.gov/pubmed/18399395)
A literature review provides an overview of what's been written about a specific topic. There are many different types of literature reviews. They vary in terms of comprehensiveness, types of study included, and purpose.
The "primary purpose is to provide the reader with a comprehensive background for understanding current knowledge and highlighting the significance of new research. It can inspire research ideas by identifying gaps or inconsistencies in a body of knowledge, thus helping the researcher to determine or define research questions or hypotheses." (https://www.ncbi.nlm.nih.gov/pubmed/18399395)