A literature review is both the process and the product.
A literature review is a descriptive, analytic summary of the existing material relating to a particular topic or area of study.
The literature review process involves a systematic examination of prior scholarly works.
Bangert-Drowns, R. (2005). Literature review. In S. Mathison (Ed.), Encyclopedia of evaluation. (pp. 232-233). Thousand Oaks, CA: SAGE Publications, Inc. doi: http://0-dx.doi.org.leopac.ulv.edu/10.4135/9781412950558.n319
Reference to prior literature is a defining feature of academic and research writing. Why review the literature?
Feak, C. B., Swales, J. M., Swales, J. M., & Feak, C. B. (2009). Telling a research story: Writing a literature review. Ann Arbor, Mich.: University of Michigan Press.
Literature Reviews: An Overview for Graduate Students by North Carolina State University Libraries