What is a Wiki?
Wikis are part of the body of collaborative methods to create and disseminate information on the internet which have come to be called Web 2.0 technologies. Wikis have an easy to learn markup language, enabling users of almost all ages and abilities to use or contribute to them. According to Ward Cunningham, creator of the first wiki, a
Wiki is a piece of server software that allows users to freely create and edit Web page content using any Web browser. Wiki supports hyperlinks and has a simple text syntax for creating new pages and crosslinks between internal pages on the fly. Wiki is unusual among group communication mechanisms in that it allows the organization of contributions to be edited in addition to the content itself. Like many simple concepts, "open editing" has some profound and subtle effects on Wiki usage. Allowing everyday users to create and edit any page in a Web site is exciting in that it encourages democratic use of the Web and promotes content composition by nontechnical users. 
Examples of Popular Wikis
- WikiWikiWeb - the first wiki (1995)
- Wikipedia - one of the largest; Wikipedia has nearly 6 million users
- Unlike the general wikis mentioned above, Archivopedia is a specialized wiki geared toward specific professions. It is currently in the beta 1.1 version and has 4,403 registered users.