A literature review is a collection of selected articles, books and other sources about a specific subject. The purpose is to summarize the existing research that has been done on the subject in order to put your research in context and to highlight what your research will add to the existing body of knowledge. Literature reviews are typically organized in some way (chronological, thematic, methodological).
Let's take a look at an example of a literature review in an article, a dissertation, and a review article.