404 error or ‘page not found’ error is a Hypertext Transfer Protocol standard response code that indicates the server was unable to find what was requested. This message may also appear when the server is not willing to disclose the requested information or when the content has been deleted.

Whenever the web page is not found, because it has either a broken or a dead link, the “404 not found” web page is generated. This code has become one of the most recognisable errors on the internet.