Wikipedia (/ˌwɪkɪˈpiːdiə/ (About this sound listen), /ˌwɪkiˈpiːdiə/ (About this sound listen) WIK-ih-PEE-dee-ə) is a multilingual, web-based, free encyclopedia based on a model of openly editable content. It is the largest and most popular general reference work on the Internet,[3][4][5] and is one of the most popular websites by Alexa rank.[6] It is owned and supported by the Wikimedia Foundation, a non-profit organization which operates on money it receives from donors.[7][8][9]

Wikipedia was launched on January 15, 2001 by Jimmy Wales and Larry Sanger.[10] Sanger coined its name,[11][12] a blend of wiki[notes 3] and encyclopedia. Initially an English-language encyclopedia, versions in other languages were quickly developed. With 5,697,782 articles,[notes 4] the English Wikipedia is the largest of the more than 290 Wikipedia encyclopedias. Overall, Wikipedia comprises more than 40 million articles in 301 different languages[14] and had 18 billion page views and nearly 500 million unique visitors each month as of February 2014.[15]

As of March 2017, Wikipedia had about 40,000 Featured Articles and Good Articles covering vital topics.[16][17] In 2005, Nature published a peer review comparing 42 science articles from Encyclopædia Britannica and Wikipedia and found that Wikipedia's level of accuracy approached that of Encyclopædia Britannica.[18] Time magazine stated that the open-door policy of allowing anyone to edit had made Wikipedia the biggest and possibly the best encyclopedia in the world and it was testament to the vision of Jimmy Wales.[19]

Wikipedia has been criticized for exhibiting systemic bias, for presenting a mixture of "truths, half truths, and some falsehoods",[20] and for being subject to manipulation and spin in controversial topics.[21] In 2017, Facebook announced that it would help readers detect fake news by suitable links to Wikipedia articles. YouTube announced a similar plan in 2018. In response, the Washington Post headlined, "Wikipedia, the ‘good cop’ of the Internet".[22]