edit 404 error
A 404 error, or "page not found" message, tells people that the web page they've requested can't be found.
A 404 error is displayed if someone clicks on a link to a website that doesn't exist anymore, or if the link is not correctly coded and doesn't lead to an actual web page. People can also get a 404 error if they mistype a website's domain name in the navigation bar of their web browser.
For more information on 404 errors, read: 404 Errors Drive Visitors Away