Systematic reviews are a structured, comprehensive approach to finding, evaluating, and synthesizing the literature on a topic. The goal is to eliminate bias in the search and selection process and to include as much high-quality literature on your topic as possible, both published and unpublished. The process for searching for and selecting literature should be documented, and will be included in the final version of the review. The systematic review process developed in the medical field, but it is increasingly being used in the social sciences as well. It is a long and involved process, typically ranging from 6 months to 2 years to complete.
The Cochrane Library, the most prominent database of systematic reviews in medicine has this to say about the process. "A systematic review attempts to identify, appraise and synthesize all the empirical evidence that meets pre-specified eligibility criteria to answer a specific research question. Researchers conducting systematic reviews use explicit, systematic methods that are selected with a view aimed at minimizing bias, to produce more reliable findings to inform decision making."
Literature Review: Literature reviews are similar to systematic reviews in that researchers provide a summary and synthesis of the extant literature on a topic. However, there is no formalized process for literature reviews; the scope of the search and search strategies will vary according to the needs of the researcher and no search protocol or inclusion-exclusion criteria need to be included in the final document. Literature reviews also typically do not include unpublished and gray literature as systematic reviews do. The advantage of a literature review is that it is much quicker and simpler to carry out than a systematic review. The disadvantage is that a literature review is less comprehensive and its selection process is vulnerable to bias. If you are an undergraduate researcher, you will likely only ever be expected to conduct a literature review.
Scoping Review: In a scoping review, researchers seek to find and categorize the research on a given topic. It follows the same rigorous, transparent search and selection process as a systematic review, but it does not synthesize the research. The topics explored in scoping reviews are often broader than those of systematic reviews, and the aim is to identify gaps in the current research on a topic rather than to answer a specific research question. The results of a scoping review can be used to identify topics for further research.
Rapid Review: Rapid reviews use the same methodology as a systematic review, but introduce some shortcuts in order to reduce the timeframe for completion. This can lead to some bias, but it is sometimes necessary for time-sensitive projects.
Umbrella Review: This is a review of systematic reviews. Umbrella reviews are useful for examining broader research questions than those of systematic reviews. In the medical context, for example, they might be useful for comparing alternative treatments for an illness in the same population.
Meta-analysis: A meta-analysis is a quantitative summary of the results of a set of studies. In a meta-analysis, researchers conduct a statistical analysis to compare the results of the included studies and identify overall trends. Systematic reviews may or may not include a meta-analysis as part of their synthesis of research.