|(English) This is an essay. It expresses the opinions and ideas of some Wikimedians but may not have wide support. This is not policy on Meta, but it may be a policy or guideline on other Wikimedia projects. Feel free to update this page as needed, or use the discussion page to propose major changes.|
Sometimes newcomers to the wiki world become a little confused about the word "wiki", especially when their only wiki experience is through Wikipedia. This is understandable, given the various differing-but-related meanings of the word. To end the confusion once and for all (hah!), here is a quick guide.
"wiki" is a generic term with several meanings:
- software that allows people to create editable websites (e.g. MediaWiki, UseModWiki)
- a website created with such software (e.g. MeatballWiki)
- the virtual community which maintains and uses such a website (ditto)
- the ideas and philosophy behind such websites
"Wiki" (or "Ward's Wiki") as a proper name refers only to the original wiki created by Ward Cunningham: 
"Wikipedia" is the particular project to create a wiki-based encyclopedia: http://www.wikipedia.org/
To further confuse things, some people spell the first term with a capital W: "When starting a Wiki, you first have to choose some Wiki software". While some folks object to this on grammatical grounds, it is fairly common.
To sum up: each individual language Wikipedia is a wiki, and the Wikipedia project as a whole is a collection of wikis, but you shouldn't say, "I added an article to Wiki today" if you were working on Wikipedia. Ward's Wiki is here.