From RFC 2068 Hypertext Transfer Protocol -- HTTP/1.1:
10.4.5 404 Not Found
The server has not found anything matching the Request-URI. No indication is given of whether the condition is
temporary or permanent. If the server does not wish to make this information available to the client, the status code
403 (Forbidden) can be used instead. The 410 (Gone) status code SHOULD be used if the server knows, through
some internally configurable mechanism, that an old resource is permanently unavailable and has no forwarding address.
temporary or permanent. If the server does not wish to make this information available to the client, the status code
403 (Forbidden) can be used instead. The 410 (Gone) status code SHOULD be used if the server knows, through
some internally configurable mechanism, that an old resource is permanently unavailable and has no forwarding address.