someone who is 404 is stupid and unable to use computers or other complicated electronic equipment - used humorously. This word comes from the usual message which appears on the Internet when a particular page you are searching for cannot be found
{i} (Internet) response error code that means that the file or document searched is not found, message that appears when a URL is not found
{s} of or pertaining to a person who is clueless, relating to a person who has no no idea