Invented by Ward Cunningham in 1995, wikis are websites which user can edit, quickly and easily, using a web browser. The name is derived from the Hawaiian word “wiki”, meaning quick; Cunningham named the software after the “wiki wiki” (quicker quick) buses at the Honolulu airport. Wikis use a simple formatting language anyone can learn in just a few minutes. The simple formatting and ease of editing via the web results in very rapidly developing websites.
The wiki software used by the Wikimedia projects is called MediaWiki. MediaWiki is developed by volunteers and Wikimedia foundation employees with the goal of creating an encyclopedia, and is an open-source project published under the GNU General Public License (GPL). In addition to the Wikimedia projects, MediaWiki has been deployed as a collaborative knowledge management tool by international corporations, organizations and universities as well as special interest groups of all kinds.
The Wikimedia server farm 
The Wikimedia projects run on a cluster of around 250 Linux servers located in Florida, Amsterdam and Seoul. During peak times the servers handle 17,500 requests per second, the average is 11,200 req/s. In June 2006 the sites had 128 million unique visitors (Source: ComScore).