When a page on your site doesn't load, an error message shall be displayed to the site visitor. Since there are different errors, there are different pages that will display, but what's standard for all of them is that they're generic and probably will have absolutely nothing that resembles the layout of your website, which can be aggravating for any visitor. This is the primary reason why web hosting service providers have introduced a feature called Custom Error Pages. For a range of different errors, visitors will see your unique content, which can be informative or amusing, based on your taste, and which will match the overall layout of your site, so the pages won't look like they aren't part of your website at all. You may use this option for numerous errors - 400 (Bad request), 401 (Unauthorized), 403 (Forbidden) and 404 (File not Found).