HTTP error 404 (not found). Most people are bound to recognize this one. A 404 error happens when you try to access a resource on a web server (usually a web page) that doesn’t exist. Some reasons for this happening can for example be a broken link, a mistyped URL, or that the webmaster has moved the requested page somewhere else (or deleted it). To counter the ill effect of broken links, some websites set up custom pages for them (and some of those are really cool).