Today is April 4th, which means that it’s 4.04 day — even in Europe where they switch their months and days around. That means it’s a perfect day to learn what a 404 status code is. Essentially, a 404 is a way for web server to return a “Page Not Found” error when a browser requests a web page that the web server doesn’t have.
A few months ago, Maile Ohye organized a “404 week” on the Google webmaster blog. You can learn what a 404 is, how to make a 404 page more useful, why you should avoid “soft” or “crypto-404s”, plus read some Q&A about 404s and see examples of good 404 pages
Happy 404 day! Today is best celebrated by making 404 jokes with friends (“404 error: beer not found”), posting pictures of good 404 errors, and general merriment.