The 404 or Not Found error message is an HTTP standard response code indicating that the client was able to communicate with the server but either the server could not find what was requested, or it was configured not to fulfill the request and not reveal the reason why. 404 errors should not be confused with "server not found" or similar errors, in which a connection to the destination server cannot be made at all.
When communicating via HTTP, a server is required to respond to a request, such as a web browser's request for an HTML document (web page), with a numeric response code and an email-like MIME message. In the code 404, the first "4" indicates a client error, such as a mistyped URL. The following two digits indicate the specific error encountered. HTTP's use of three-digit codes is similar to the use of such codes in earlier protocols such as FTP and NNTP.At the HTTP level, a 404 response code is followed by a human-readable "reason phrase". The HTTP specification