The error page is the message displayed to the visitor when an error occurs in retrieving the webpage they requested for. Error message is also displayed when a server error occurs.
The most common errors are-
1) 404 Not Found is displayed when the requested URL is not found on the web server. Causes can be-
a)The link does not exist on web.
b)The page was removed or re-named.
c)The user made a mistake when typing the URL.
2) 403 Forbidden is displayed when the user requests for a page he is not allowed to i.e. pages which the general users are not allowed to access.
3) 503 Service Unavailable is displayed when the server is unavailable or overloaded or down.
The custom error page is the error page (this page matches the theme and design of the site) in response to error occurring in the site.