A mechanism used by Wikipedia to discourage addition of articles in the encyclopedia.
The criteria for speedy deletion specify the limited cases in which administrators may, at their discretion, bypass deletion discussion and immediately delete Wikipedia pages or media. These criteria describe the only cases where there is broad consensus supporting summary deletion of articles and other content. Deletion is reversible, but only by administrators, so other deletions occur only after discussion. Speedy deletion is intended to reduce the time spent on deletion discussions for articles with no practical chance of surviving discussion.
Even if the principle seems to be founded, arbitrary decisions might discourage people to participate and undermine wiki adoption.
You won't find an article on Wikidot, a wiki farm, despite efforts of the wikidot community of users to add an article in Wikipedia and despite that Wikidot is alexa-ranked in 5th position in a table from http://en.wikipedia.org/wiki/Wiki_farm