404 Error Page
A 404 error page is the page served when a requested URL does not exist – because of a typo, a deleted page or an outdated link – and it should return the actual HTTP status code 404. Redirecting silently to the home page instead stops search engines from recognising that the page has really gone.
In practice
A good 404 page offers helpful navigation, such as a search function or links to popular pages, instead of showing a bare error message. Checking regularly for broken internal links also stops users from ending up on such pages in the first place.