Popular Mechanics:

It’s the bane of every web surfer, the internet’s version of fingernails on the chalkboard. Click almost any link that dates back to pre-2005 and brace for the inevitable: “HTTP 404 Not Found.”

Anyone who’s spent time near an internet connection is familiar with the 404 error, a webserver’s way of saying you’ve reached a dead end. What’s less well known is that this very error is what allowed the World Wide Web to exist in the first place.

I didn’t realize the number 404 actually stood for something.