A literature review (or "lit review," for short) is an in-depth critical analysis of published scholarly research related to a specific topic. Published scholarly research (aka, "the literature") may include journal articles, books, book chapters, dissertations and thesis, or conference proceedings.
A solid lit review must:
be organized around and related directly to the thesis or research question you're developing
synthesize results into a summary of what is and is not known
identify areas of controversy in the literature
formulate questions that need further research
View the video for a brief explanation of lit reviews.