ci·tá·tion: noun: A quoting of an authoritative source for substantiation.
--The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
A citation is a brief description of one specific information source, usually appearing in a bibliography, list of references, or a database. It includes enough information to permit the reader to find the source and may appear in a number of variant formats, e.g. American Psychological Association (APA), Modern Language Association (MLA), Council of Biology Editors (CBE), or Chicago Style (CMS).
A citation is made of parts, each part indicating specific information about the source. You can usually tell what type of source is being described by looking carefully at the citation. The citation below (in APA style) refers to an article found in a journal called Climatic Change.