Glossary · Hosting and delivery
404 Not Found
The HTTP response used when the server cannot find the requested resource.
Also called: 404, 404 error
Definition
404 Not Found means the server received the request but cannot locate the requested resource. It may result from a mistyped URL, deleted page, broken internal link, incomplete migration, or route that never existed.
Why it matters
Unexpected 404s can interrupt customer journeys, waste earned links, and prevent people or crawlers from reaching useful replacement content.
Common misunderstanding
A branded page-not-found message is not enough if the server incorrectly returns 200, and not every 404 should redirect to the homepage.
Ownership implications
Maintain a record of important retired URLs, valid replacements, and intentionally unavailable paths.
Business implications
Prioritize 404s that affect real traffic, valuable links, forms, campaigns, or core navigation instead of chasing every automated request.
Related terms
Related system family: Hosting & Release
Sources
- HTTP response status codes (opens in a new tab) · MDN Web Docs
- How the web works (opens in a new tab) · MDN Web Docs
Last reviewed July 16, 2026