Wikipedia is a free, web-based, collaborative, multilingual encyclopedia project supported by the non-profit Wikimedia Foundation. Its 20 million articles (over 3.8 million in English) 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 July 2011, there are editions of Wikipedia in 282 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 technology for creating collaborative websites, from the Hawaiian word wiki, meaning "quick") and encyclopedia.
Wikipedia's departure from the expert-driven style of encyclopedia building and the large presence of unacademic content has often been noted. 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.
Although the policies of Wikipedia strongly espouse verifiability and a neutral point of view, critics of Wikipedia accuse it of systemic bias and inconsistencies (including undue weight given to popular culture), and because it favors consensus over credentials in its editorial processes, its reliability and accuracy are also targeted. Other criticisms center on its susceptibility to vandalism and the addition of spurious or unverified information; though some scholarly work suggests that vandalism is generally short-lived. A 2005 investigation in Nature showed that the science articles they compared came close to the level of accuracy of Encyclopędia Britannica and had a similar rate of "serious errors".