Short definition
The response a server gives when a page cannot be found.
Beginner In plain English
A 404 is the "page not found" message. It happens when a page was deleted, moved without a redirect, or the link has a typo.
Professional How pros use it
404s for truly removed content are normal. Problems arise when important pages 404, internal links point to 404s, or valuable backlinks land on them; redirect those to the closest relevant page.
Examples
- /sale/ returning 404 after a promotion ended.
- A typo in a navigation link.
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