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 23 million articles, over 4.1 million in the English Wikipedia 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 active contributors. As of November 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. In 2011, Wikipedia received an estimated 2.7 billion monthly pageviews from the United States alone.
Wikipedia was launched on January 15, 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 2006, Time magazine recognized Wikipedia's participation in the rapid growth of online collaboration and interaction by millions of people around the world, in addition to YouTube, MySpace, and Facebook. Wikipedia has also been praised as a news source due to articles related to breaking news often being rapidly updated.
The open nature of Wikipedia has led to various concerns, such as the quality of writing, the amount of vandalism and the accuracy of information. Some articles contain unverified or inconsistent information, though a 2005 investigation in Nature showed that the science articles they compared came close to the level of accuracy of Encyclopædia Britannica and had a similar rate of "serious errors". Britannica replied that the study's methodology and conclusions were flawed, but Nature reacted to this refutation with both a formal response and a point-by-point rebuttal of Britannica's main objections.