A citation is a brief reference to a specific information source such as a book, a journal article, or a website, which acknowledges an original idea expressed therein and provides a means of locating the original source. In general, a citation includes both a notation in the body of a text and an entry in a list of sources following the text.
A citation style is a set of guidelines for formatting and organizing citations. Although there exist many different citation styles to suit different purposes, most academic research papers adhere to one of three major styles: American Psychological Association (APA), Chicago/Turabian, or Modern Language Association (MLA).
Use the style recommended or required by your instructor. If your instructor does not specify a style, choose one based on the discipline or field about which you are writing: