In 1992 Tim Berners-Lee defined all the HTTP (Hypertext Transfer Protocol) codes based on the FTP (File Transfer Protocol) status codes. If you break it down,
List of HTTP status Code
So, in brief you can say that, the 404 or Not Found error message is a Hypertext Transfer Protocol (HTTP) standard response code, in computer network communications, to indicate that the client was able to communicate with a given server, but the server could not find what was requested. The web site hosting server will typically generate a "404 Not Found" web page when a user attempts to follow a broken or dead link; hence the 404 error is one of the most recognizable errors encountered on the World Wide Web.
- The first '4' indicates the error is a client error
- Second the '0' indicates a general syntax error
- Final '4' refers to the specific error code in the '4xx' group of error codes.
List of HTTP status Code
So, in brief you can say that, the 404 or Not Found error message is a Hypertext Transfer Protocol (HTTP) standard response code, in computer network communications, to indicate that the client was able to communicate with a given server, but the server could not find what was requested. The web site hosting server will typically generate a "404 Not Found" web page when a user attempts to follow a broken or dead link; hence the 404 error is one of the most recognizable errors encountered on the World Wide Web.