The ErrorDocument directive sets up default messages or static pages to be served when an HTTP error is encountered.
ErrorDocument 500 /static_errors/500.html ErrorDocument 404 /static_errors/404.html ErrorDocument 401 /signup
Error message really suck for end users, especially when they are taken to an unstyled, text-only page. Fortunately, Apache provides the ability to configure how those messages are displayed. Perhaps the best way to handle this is through a custom error document, which can be configured through the ErrorDocument directive.
When you're putting together your site, make sure that you create some static HTML pages that follow the styling set up by your larger project, and create reassurance for your site's visitors that they are in the right place, that the thing that has just happened isn't their fault, and a set of next steps they can follow to find out more.