The literature review is an integral part of any research project and is undertaken as a means of surveying what research has been conducted previously on a particular topic.
There are many reasons for conducting a literature review, but one of the primary reasons is to establish a base line of what is already known on a topic before exploring the topic any further. The review typically involves a search of any previously published or presented materials that might have relevance to a prospective new study.
If the point of a research project is solely to review what has already been written on a topic, the resulting article is termed a "survey of the literature" or a "literature survey" or even a "literature review." In this case, the article is complete in itself and does not delve into anything new regarding the topic. A literature survey might end with a discussion of what work is still needed to further develop knowledge of a particular topic, but it does not, itself, flesh out any of those ideas. Articles of this type can be highly beneficial to someone seeking to launch an original study; literature surveys have already laid some of the groundwork for a prospective researcher's own literature review.
When the survey serves as the initial step that precedes a further investigation of an idea or ideas about a topic, then that review of the literature sets the stage for the presentation of original research. Original research usually involves the selection of a methodology for examining a topic and may include the gathering of data that can be further analyzed to arrive at assumptions about the topic. Data may be derived from the examination of human subjects, from conducting surveys or assessments, from the study of particular species of plants or animals, from the systematic scientific measurement of any physical phenomena, from nearly anything that can be documented and analyzed. Again, the whole point of launching an original study is to learn something new about a topic. Research typically begins with what is known (the literature review) and progresses into analyzing, through the observation and analysis of data, what is yet to be known through further study.
Both the literature survey and the original study are considered academic articles, as opposed to popular articles. Both involve research in order to come to a better understanding of a topic.