An asinine Web craze, primarily among webloggers and users on systems like LiveJournal and DeadJournal.
The user visits the Web page, and answers typically a dozen facetious, multiple choice questions. Often these will have only yes or no answers; if the designer's chosen to spend a little more time, there might be six or seven possible results for each question.
The system then picks an entirely farcical personality type for the user. Often there will be an accompanying graphic for the user to stick on their Web page, so that other people will see it, take it, and stick the graphic on their Web pages.
They can thus be described as viral memes. It's not uncommon for an unknown Web personality test to get a million hits within a month of launch, possible making money through banner ads or popups. Sites operating in such a way include http://emode.com/.
It should also be noted that because the hosting site gets hundreds of thousands of links pointing to it, it's an easy way for them to get a good position on Google.
There have been thousands, but some tests have included: