If a page on your website doesn't load, an error message will be shown to the website visitor. Since there are different errors, there are different pages that will show up, but what is common for all of them is that they're generic and almost certainly will have nothing that is similar to the layout of your site, which may be aggravating for any visitor. That is the primary reason why web hosting providers have introduced a function referred to as Custom Error Pages. For a wide variety of different errors, visitors shall see your custom made content, which could be informative or funny, in accordance with your personal preference, and that will match the design of your site, so the pages will not appear as if they aren't part of your website at all. You can use this option for many errors - 400 (Bad request), 401 (Unauthorized), 403 (Forbidden) and 404 (File not Found).