404 Error
The status for a URL that does not exist. Healthy in itself; harmful when it is wrong or soft.
A 404 error is the status code a server returns when the requested URL does not exist. A 404 is correct and healthy for a page that was never real; it becomes a problem when a page people still link to starts returning one, because the links pointing at it stop passing value and visitors hit a dead end.
Definition
A 404 is the HTTP status meaning the requested URL does not exist. It is a legitimate, healthy response — a site with no 404s is usually a site redirecting things it should not.
Two variants cause real damage. A soft 404 returns status 200 with "page not found" content, so crawlers keep the URL and keep re-fetching it. And a 404 served by mistake — a data-fetch timeout treated as "missing", say — removes a live page from search until the crawler returns.
410 Gone is the stronger statement: the page existed, it is deliberately removed, do not come back. Use it when you mean it.
Why It Matters
404s reachable from internal links or listed in a sitemap are the ones that matter: they waste crawl budget, break the path link equity was taking, and tell Google the site is not maintained. A 404 nobody links to is harmless.
The dangerous case is a transient 404 on a page that exists. Search engines are conservative about re-checking, so a brief outage can cost visibility for far longer than the outage lasted.
Example
Two checks worth running: crawl your own sitemap and confirm every URL returns 200 — a sitemap advertising 404s is a direct quality signal to Google — and confirm your 404 page really returns status 404, not 200 with apologetic text.
Related Tools
Know the term.
Check your own site.
A free audit tells you whether this is currently costing you score points — and exactly what to change.
Run a free audit