Differences between Wikipedia, Wikimedia, MediaWiki, and wiki

Confused about the difference between MediaWiki, Wikimedia, Wikipedia and Wiki?

wiki
wiki is a generic term which is used to describe a certain kind of collaborative website that can be edited by any user and/or visitor.
 * wiki (as an adjective), the Wiki Way, and the antonym un-wiki are also used to describe the community-oriented philosophy that goes with such a system (e.g. "that's not a very wiki way of doing things").
 * Wiki (with a capital 'W') and WikiWikiWeb are used to refer to the Portland Pattern Repository, which was the first wiki to be created.
 * wiki software and wiki engine are terms referring to pieces of software that power wiki-based websites. There are many different types of wiki software; some very simple, others enhanced with specific advanced features. See also: Wikipedia's entry on "wiki software" or the Portland Pattern Repository's "canonical" list of wiki engines.

For a more complete definition, see Wikipedia's entry on "wiki".

Wikimedia
Wikimedia is the collective name for a group of inter-related projects, including Wikipedia, Wiktionary, Wikisource, Wikibooks, and others, which aim to use the collaborative power of the Internet, and the wiki concept, to create and share free knowledge of all kinds. Like "Wikipedia", "Wikimedia" is a trademark, and should not be used for projects which are not officially affiliated. Wikimedia is also used as a shortened form of The Wikimedia Foundation.


 * The Wikimedia Foundation is the non-profit organization which funds and manages these projects. For more information, see the Foundation's homepage
 * The term Wikimedia servers is often used, referring to the computer hardware on which all Wikimedia projects are hosted. The servers are supported primarily by volunteers, many of whom also work on the MediaWiki software (see below); the Wikimedia servers are not available for hosting projects not run by the Wikimedia Foundation, with the exception of some non-official IRC servers and other non-Foundation-approved installations made by those with access to the servers. See also: Wikimedia servers.
 * The Wikimedia Meta-Wiki, commonly referred to as Meta, is the wiki used to discuss issues which affect all Wikimedia projects; it is also used for discussing the development of the MediaWiki software (see below), since this is often tightly linked to the needs of Wikimedia projects. See also: About.
 * Meta should not be confused with MetaWiki, a search engine that is not part of the Wikimedia group of projects.

See also: Wikimedia, The encyclopedia article on Wikimedia.

MediaWiki
MediaWiki is the particular wiki engine developed for and used by Wikipedia and the other Wikimedia projects. It is freely available for others to use (and improve), and there are many copies in use by all sorts of projects around the world.

See also How does MediaWiki work?, Sites using MediaWiki.