404 Error Pages
When we browse the web and a particular page can not be found by the browser, we are served an error page by the server of the web site we are visiting, called 404 (which means that the page does not exist).
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 404 Error - the first 4 indicates a client error such as a mistyped URL. The middle 0 refers to a general syntax error. The last 4 just indicates the specific error in the group of 40x, which in this case is
These customized 404 error pages serve the purpose of offering the web site user an apology or alternative way of finding back into the content the web site deals with, or both.
Each response code has an associated string of English text that must also be present; response code 404's associated string is "Not Found". When sending a 404 response, web servers usually include in the response message a short HTML document that mentions both the numeric code and this string. These messages can be customized on a large number of such servers to display a page that could be of more help than a default. For example, this can be achieved in Apache by placing a .htaccess file on the Web server or editing httpd.conf.
A 404 error is often returned when pages have been moved or deleted. In the first case, a better response is to return a 301 Moved Permanently response, which can be configured in most server configuration files, or through URL rewriting; in the second case, a 410 Gone should be returned. Because these two options require special server configuration, most websites do not make use of them.