Broadly, a citation is a reference to a published or unpublished source (not always the original source). More precisely, a citation is an abbreviated alphanumeric expression (e.g. [Newell84]) embedded in the body of an intellectual work that denotes an entry in the bibliographic references section of the work for the purpose of acknowledging the relevance of the works of others to the topic of discussion at the spot where the citation appears. Generally the combination of both the in-body citation and the bibliographic entry constitutes what is commonly thought of as a citation (whereas bibliographic entries by themselves are not).

Citation has several important purposes: to uphold intellectual honesty, to attribute prior or unoriginal work and ideas to the correct sources, to allow the reader to determine independently whether the referenced material supports the author's argument in the claimed way, and to help the reader gauge the strength and validity of the material the author has used.

Wikipedia (ⁱ/ˌwɪkɨˈpiːdiə/ or ⁱ/ˌwɪkiˈpiːdiə/ WIK-i-PEE-dee-ə) is a free, collaboratively edited and multilingual Internet encyclopedia supported by the non-profit Wikimedia Foundation. Its 22 million articles (over 0 million in English alone) have been written collaboratively by volunteers around the world. Almost all of its articles can be edited by anyone with access to the site, and it has about 100,000 regularly active contributors. As of June 2012, there are editions of Wikipedia in 285 languages. It has become the largest and most popular general reference work on the Internet, ranking sixth globally among all websites on Alexa and having an estimated 365 million readers worldwide. It is estimated that Wikipedia receives 2.7 billion monthly pageviews from the United States alone.

Wikipedia was launched in January 2001 by Jimmy Wales and Larry Sanger. Sanger coined the name Wikipedia, which is a portmanteau of wiki (a type of collaborative website, from the Hawaiian word wiki, meaning "quick") and encyclopedia. Wikipedia's departure from the expert-driven style of encyclopedia building and the presence of a large body of unacademic content have received extensive attention in print media. In its 2006 Person of the Year article, Time magazine recognized the rapid growth of online collaboration and interaction by millions of people around the world. It cited Wikipedia as an example, in addition to YouTube, MySpace, and Facebook. Wikipedia has also been praised as a news source because of how quickly articles about recent events appear. Students have been assigned to write Wikipedia articles as an exercise in clearly and succinctly explaining difficult concepts to an uninitiated audience.