A citation, also called a reference, uniquely identifies a source of information, e.g.: Wikipedia's verifiability policy requires inline citations for any material challenged or likely to be challenged, and for all quotations, anywhere in article space. A citation or reference in an article usually has two parts. In the first part, each section of text that is either based on, or quoted from, an outside source is marked as such with an inline citation. This is usually displayed as a superscript footnote number: [1] The second necessary part of the citation or reference is the list of full references, which provides complete, formatted detail about the source, so that anyone reading the article can find it and verify it. This page explains how to place and format both parts of the citation. Each article should use one citation method or style throughout. If an article already has citations, preserve consistency by using that method or seek consensus on the talk page before changing it (the principle is reviewed at § Variation in citation methods). While you should try to write citations correctly, what matters most is that you provide enough information to identify the source. Others will improve the formatting if needed. See: "Help:Referencing for beginners", for a brief introduction on how to put references in Wikipedia articles; and cite templates in Visual Editor, about a graphical way for citation, included in Wikipedia.