xkcd is a webcomic that makes its home on xkcd.com. And what a webcomic! I think it's consistently better than pretty much any you'll find in your local paper.
How many?
As of February 27, 2007, there have been 227, A new one comes out each Monday, Wednesday, and Friday.
Who? About?
You mean who are the characters or who wrote it? Well, I guess it's kind of the same. The characters are stick figures and often represent the author, Randall Munroe. He's a physicist who used to work at NASA. With robots. Big stompy Martian-killing robots of DOOM! (But they're top secret, so you didn't hear it from me.)
Redalien adds: 'Randall is also a lovely man! He's given the computer science society at the university of bristol permission to reproduce one of his comics for profit. The others are, of course, creative commonsed.' (links mine)
The content is the musings, fears (especially of velociraptors), and thoughts of the author, someone cooler than any of us. He's a geek--he sees math and physics everywhere. Sometimes they're very sweet, but unlike some comics, he remembers to be funny at the same time. To be honest, it reminds of a geeky Pearls Before Swine1. And who doesn't like Pearls Before Swine? Sometimes it reminds me a little of Calvin and Hobbes.2 Other times it's just what it is. (phraggle says it reminds him of E2: 'geeky and beautiful'.)
Okay, maybe you won't fully understand every joke. You'll laugh anyway.
Oh, and just so you know, always check for title attributes on the comic. This can be done by holding the mouse cursor over it. Sometimes there's an brief explanation of the joke. Usually, just relevant line. It's like a minijoke to go with the comic. Delightful!
The Name
It's not an initialism. From the about page: 'It's just a word with no phonetic pronunciation. It stands for the comic and everything the comic stands for!' And that's just what a name is supposed to do, is it not?
- 1 Examples: http://xkcd.com/c193.html and http://xkcd.com/c108.html
- 2 Example: http://xkcd.com/c209.html