A Literature Review is a systematic review of the published material, or scholarly writings, on a specific topic or research question.
The primary goal is analysis - and not simply summarization - of these scholarly writings. This analysis serves to provide background information on your topic and detail the connection between those writings and your research question. After all, we cannot know where we're going until we know where we've been.
Literature reviews can be a stand-alone paper, or can be a section of a research paper.
Laurence Machi and Brenda McEvoy's Literature Review model emphasizes critical thinking throughout the six-step workflow described in their book.