A citation is a reference that allows you to acknowledge the sources* you use in a formal academic paper, and enables a reader to locate those sources through the key information it provides.
Citations are placed both in the text and in an organized list at the end of the text. The format of the citations can vary depending on the citation style that is used. If a footnote or endnote system is used, citations can be self-contained without an organized list.
*Source material might come from books, journal articles, speeches, websites, on-line articles, films, government publications, legal proceedings, maps, and so on.