A. From Wikipedia (http://en.wikipedia.org): A wiki is a page or collection of Web pages designed to enable anyone who accesses it to contribute or modify content, using a simplified markup language.^[1][2] Wikis are often used to create collaborative websites and to power community websites. The collaborative encyclopedia Wikipedia is one of the best-known wikis.^[2] Wikis are used in business to provide intranets and Knowledge Management systems. Ward Cunningham, developer of the first wiki software, WikiWikiWeb, originally described it as "the simplest online database that could possibly work".^[3]

There are several Wikis available.

One that is from the makers of the Wiki, is MediaWiki

MediaWiki is a free software wiki package originally written for Wikipedia. It is now used by several other projects of the non-profit Wikimedia Foundation and by many other wikis, including this website, the home of MediaWiki. 

Joomla CMS has an extension that will imbed the wiki into your website, this will mantain the wiki and websites function, look and feel.