404 Error

A 404 error is a HTTP standard response code indicating the browser was able to communicate with a given server, but the server could not find the requested page.
Generally, any code within 400 to 499 indicates that the page didn’t load. The 404-response code is the only one that carries a specific meaning – that the page is actually gone and probably isn’t coming back anytime soon.
Search Engine Journal

Resources

Glossary Topics