Wikipedia, free Internet-based encyclopaedia, started in 2001, that operates under an open-source management style. It is overseen by the nonprofit Wikimedia Foundation. Wikipedia uses a collaborative software known as wiki that facilitates the creation and development of articles.

Wikipedia was launched on January 15, 2001 as a single English-language edition at www.wikipedia.com, and was announced by Sanger on the Nupedia mailing list. The name originated from a blend of the words wiki and encyclopedia. Its integral policy of "neutral point-of-view" was codified in its first few months.

"Wiki" (pronounced [wiki]) is a Hawaiian word meaning "quick". The online encyclopedia project Wikipedia is the most popular wiki-based website, as well being one of the most popular websites on the entire internet, having been ranked consistently as such since at least 2007.

As of 26 May 2024, there are 6,827,580 articles in the English Wikipedia containing over 4.5 billion words (giving an average of about 668 words per article). The total number of pages is 60,757,657. Articles make up 11.24 percent of all pages on Wikipedia.