To bring this node into the 202nd decade...
" SCIENCE. It works, bitches. "
— xkcd 54, wherein a graph of cosmic microwave background radiation is portrayed.
xkcd, owned and operated by Randall Munroe, is a webcomic containing witty and often geeky humour. At the time of writing, the number of comics is well over a thousand and counting. It's the kind of comic to which you say "haha, that's so true" more than anything, though it does have moments that fall under the banner of tragic, hilarious, memorable, or simply badass. It also adopts the gimmick of alt-text (viewed by hovering the mouse over the image for a few moments and reading the displayed tooltip) for every comic, providing an additional joke or fact for the entertainment of those who've remembered to check it.
Its reputation among the net-savvy is legendary. One unofficial claim is that there is an xkcd comic for everything, every situation you have ever been in—this claim has yet to be refuted. It has also influenced a lot of internet culture, being the humour fountain that it is: Cory Doctorow was said to sport a cape and googles when blogging in one comic, and subsequently the real Cory Doctorow dressed up like this for a charity event due to the sheer popularity of the idea. As well, terms and ideas like 'blag', 'blogosphere', 'geohashing', and probably a bunch of others find their origins at this site.
Interspersed amongst the jokes, tricks, and thinly-veiled life lessons, you can also find infographics on current events. From a comparison chart of different radiation emission levels, to an analysis of the numbers of Google hits for "<game>" vs. "strip <game>", to a recent one on the history of US electoral leanings. An early one maps out IPv4 addresses, and then another maps out the internet itself. Even topics like 'How to make people feel old' are covered. Everything is thoroughly researched, some jokes are thrown in when it's tasteful, it's beautiful. And the best part is that it meshes seamlessly with the style of comic that Randall has running.
But the webcomic isn't the only thing on the site! Randall has a blag, where he makes posts about his life and what he does or finds sometimes. There's a bunch of humourous excerpts from the National Hurricane Center discussion bulletin, the morbid actuarial script that he actually used for some of his comics, and various other adventures and announcements in and/or about his life. There's a store, if you're looking for some velociraptor-themed swag. And Randall's recently launched the What If? section, wherein readers send in crazy questions about physics, and once a week, Randall simultaneously blows everything out of proportion in the most humourous fashion the question allows for, and takes us through a blow-by-blow of how and why what happens, happens. It's like the comic, but longer-winded and more educational.
A few selected comics:
So, what might xkcd stand for, you ask? It does not stand for any words—it stands for principles.