A "wiki" is a website that allows its users to add, change or delete content within its pages. The term is used to describe collaborative authoring applications: the most well known being "Wikipedia".
Wikis are often powered by a wiki software or a wiki hosting site. These sites are typically intuitive and easy to use: designed so that anyone can participate in them. Most wiki sites require users to register and often contain levels of access to different parts of the site.
Wikis are often used as community websites and note-taking services.
(About wikis was created at Tyndale University. Permission to use was given by Mark Mueller.)