Today is April 4th, which means that it’s time to get geeky and celebrate Webmasters’ Day. Essentially, the 404 error is a way for web server to return a “Page Not Found” error when a browser can’t find the requested page.
The 404 error message is a HTTP standard response code indicating that a user attempts to follow a broken or dead link.
Here are a few other error code pages:
See more at HTTP.cat