"Nielsen//NetRatings reports that Wikipedia's unique audience increased from about 3.3 million in September 2004 to 12.8 million by September 2005. Wikipedia, which bills itself as 'the free encyclopedia,' is a constantly growing and changing compendium of information about hundreds of thousands of topics. Unlike standard encyclopedias, the content comes from the Web site's users, who can create, edit and delete information on the site at will. The site has administrators who monitor these changes and prevent, or correct, abuse or incorrect updates."
