Differences between Wikipedia, Wikimedia, MediaWiki, and wiki/en

Confused about the differences 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; it is not a proper noun.
 * 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 description, 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.

Wikimedia is also the short name for the Wikimedia Foundation, a non-profit organization headquartered in San Francisco that runs these projects.
 * The term Wikimedia servers is often used, referring to the computer hardware on which all Wikimedia projects are hosted. The servers are run by employees of the Wikimedia Foundation, many of whom also work on the MediaWiki software (see below).
 * Wikimedia Deutschland, Wikimedia Russia etc. are not part of Wikimedia Foundation, but usually are friends of it.
 * The Wikimedia Meta-Wiki, commonly referred to as Meta, is the wiki used to discuss issues which affect all 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.

Wikipedia
Wikipedia? Wikipedia is [//www.wikipedia.org/ Wikipedia], The Free Encyclopedia. Who doesn't know Wikipedia? ;)

MediaWiki
MediaWiki is software. 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, How to become a MediaWiki hacker.

Video

 * [//www.youtube.com/watch?v=gXD1TRGafQ0 The State of Wikipedia] on YouTube