1 Me: Gosh, wikis are taking over the web.
2 {me looking astonished at a web site}
3 Me: {reading} "The CIA World FactWiki"?
4 Me: {reading} "The official source for US Government profiles of countries and non-self-governing territories around the world that anyone can edit!"

Well, if you don't know what a wiki is, you probably never read these annotations anyway, so...

The CIA World Factbook is an official publication of US Government profiles...

Oh heck, it's what it says in the comic. Except you can't edit it.

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2016-01-15 Rerun commentary: Nowadays there are all sorts of weird and wonderful wikis.

Starting from Conspiracy Wiki I hit the "random wiki" button a few times and got:

• TARDIS Data Core
• Answerpedia
• Creepypasta Wiki
• Digimon Wiki
• Mixels Wiki
• Academic Jobs Wiki
• Logopedia

There's even an Irregular Webcomic! Wiki!

Many of these wikis are dedicated to various popular media franchises, as this seems to be a thing that many wiki-savvy people like to spend their time doing. These are just ones located on Wikia, though - there are also other wikis hosted on different servers, such as the Esoteric Programming Languages wiki and of course TV Tropes. There are also some rather infamous wikis, which I won't name here - if you know the ones I mean you'll know why I don't.

On the more academic side, there is the STEMWiki family of wikis hosted by the University of California Davis, including PhysWiki, ChemWiki, and MathWiki, among others. There's also WikiArt and WikiGallery.

There's pretty much a specialised wiki for anything you're interested in. And if not, you can easily make your own, so there's no excuse not to be.