"Citation needed" is a tag added by Wikipedia editors to unsourced statements in articles requesting citations to be added. The phrase is reflective of the policies of verifiability and no original research in Wikipedia and has become a general Internet meme.
By Wikipedia policy, editors should add citations for content, to ensure accuracy and neutrality, and to avoid original research. In 2005, Chris Sherlock, a Wikipedia editor with the username Ta bu shi da yu, created the "citation needed" template, to be added to statements without a citation that needed verification. The template is used frequently—as of December 2019[update], over 400,000 articles in the English Wikipedia are marked with the template.
In 2007, the webcomic xkcd published a comic called "Wikipedian Protester". In the comic, a group of people are listening to a politician's speech, and a protester raises a placard which says "", in Wikipedia's characteristic blue color for links. This is the first known use of the term outside Wikipedia. This also spawned a meme, on the "explain xkcd" wiki, of placing a "citation needed" tag after obvious statements. Randall Munroe, the creator of xkcd, has also used "" in similar fashion throughout his blog What If?, and, consequently, in the book published as a compilation of the blog's entries.
In 2008, Matt Mechtley created stickers with "", encouraging people to stick them on advertisements. This kind of graffiti has been dubbed "wikiffiti". Quickly becoming an Internet meme, "" appeared not only on billboards, but also some internet kuso pictures. For example, someone doctored a photograph of George W. Bush's Mission Accomplished speech to place a "" label under the "mission accomplished" banner.
In 2010, American television hosts Jon Stewart and Stephen Colbert led the Rally to Restore Sanity and/or Fear at the National Mall in Washington, D.C. Some "protesters" held placards with "".
In 2011, German defence minister Karl-Theodor zu Guttenberg was facing accusations that he plagiarized his doctoral thesis. Protesters with "" placards called attention to the many contexts in his thesis where his sources were not labeled.
In 2017, the hosts of the Cognitive Dissonance podcast and the hosts of The Scathing Atheist podcast began working on a weekly podcast with the name Citation Needed. In the podcast, one of the cast is assigned to read an article on Wikipedia and prepares a comedic essay summarizing the article.
The Sun is really bright  and its light illuminates the Earth.[note 1]
The Sun is really bright, and its light illuminates the Earth.