How does the code on StackOverflow's 404 page work? (Pic included)

Question

Everybody's seen this before, but what is this code? I don't even know what language to tag this with. Could somebody decipher it?

Note- I would post this on meta but it is a programming question, just pretend I had said "I found this mystery code somewhere..."

Answer 1

All the lines except line four are commented with #. Line four simply prints 404.

And here I thought it was some crazy #define macro.

Original posting is here: https://meta.stackexchange.com/questions/27112/amusing-404-page-not-found-images-for-trilogy-sites

Also seen here: https://meta.stackexchange.com/questions/28625/whats-the-joke-in-the-stack-overflow-404-page-code