Wikipedia is a free content online encyclopedia written and maintained by a community of volunteers, known as Wikipedians, through open collaboration and the use of the wiki-based editing system MediaWiki. Wikipedia is the largest and most-read reference work in history.

On January 15, 2001, Wikipedia was launched as a feature of Nupedia.com, but, following objections from the advisory board, it was relaunched as an independent Web site a few days later.

There are currently 47,456,083 Wikipedia accounts, of which 120,533 have made at least one edit during the last month. Wikipedia is in the palm of your hand—all you need to do is edit an article. Wikipedians are volunteers who contribute to Wikipedia by editing its pages, unlike readers who simply read the articles.

The name was suggested by Sanger on 11 January 2001 as a portmanteau of the words wiki (Hawaiian for "quick") and encyclopedia. The wikipedia.com and wikipedia.org domain names were registered on 12 and 13 January, respectively, with wikipedia.org being brought online on the same day.