404 page is what someone sees when they open a URL on your site that is not a page — deleted, renamed, or never published. The server answers with status 404, “not found.” Your job is the screen: say the page is missing, and offer a way forward.
It is one kind of error state, not the whole category. A declined payment and a failed form validation are errors too. A 404 is specifically a missing address. It is also not a landing page: a landing page exists to convert. A 404 exists because the path failed. A canonical URL tells search engines which duplicate to keep. It does not rescue a link that points nowhere. Clean web architecture, a current sitemap, and breadcrumbs cut how often people hit the dead end. Usability is the recovery: search, a few real links, a path home.
A real-life example of a 404 page
An Atlanta restaurant renames its menu URL. An old Instagram link still uses the first address. A blank “Not Found” dumps the hungry visitor. A useful 404 says the menu moved, links to dinner, and offers the phone number. Same idea as a host who walks you to the right table instead of shrugging.
Keep the page on brand, and point somewhere real. How to design one: the perfect 404 page. For why the recovery copy matters: What Is Usability?.