The term literature review can either refer to a type of research paper that relies on existing scholarly literature to help develop new ideas, or it can refer to a portion of a paper, in which a review of the existing literature serves to inform an original study that the paper documents. In the first case, the literature review serves as its own type of research method. In the second case, the primary research method will depend on the type of study being conducted and the data collected from that study.
Think of scholarly papers like a conversation. A paper takes a look at what people are saying on a particular topic and then adds something new to the conversation based on their own research. A literature review is how scholars get caught up on the conversation so they will know what to ask or say next.
A literature review can be a simple summary of the sources, but it usually has an organizational pattern that combines both summary and synthesis.
A summary is a recap of the important information of the source, but a synthesis is a re-organization of that information that results in new ideas.
A literature review is important because it: