A WikiWiki (usually known as a wiki) is a web application which enables communities to collaboratively add, modify, or delete the content of a web site. Text is written using a simple markup language (called WikiMarkup) or a rich-text editor.

A single page in a wiki website is referred to as a "wiki page", while the entire collection of pages, which are usually well interconnected by hyperlinks, is "the wiki". A wiki is essentially a database for creating, browsing, and searching through information. A wiki allows non-linear, evolving, complex and networked text, argument and interaction.

Ward Cunningham, the developer of the first wiki software, WikiWikiWeb, originally described it as "the simplest online database that could possibly work". "Wiki" comes from the Hawaiian word "wikiwiki" meaning "fast" or "quick". Ward Cunningham and co-author Bo Leuf, in their book The Wiki Way: Quick Collaboration on the Web, described the essence of the Wiki concept as follows:

See: the original WikiWikiWeb or Wiki on Wikipedia