A literature review is a systematic review of the published literature on a specific topic or research question designed to analyze-- not just summarize-- scholarly writings that are related directly to your research question. That is, it represents the literature that provides background information on your topic and shows a correspondence between those writings and your research question.
NCSU Libraries http://www.lib.ncsu.edu/tutorials/litreview/
Keep in mind that a literature review defines and sets the stage for your later research. While you may take the same steps in researching your literature review, your literature review is not:
A literature review is important because it: