404 er·ror

/fôr ō fôr ˈerər/

noun

The HTTP 404, 404 Not Found, 404, 404 Error, Page Not Found, File Not Found, or Server Not Found error message is a Hypertext Transfer Protocol (HTTP) standard response code, in computer network communications, to indicate that the browser was able to communicate with a given server, but the server could not find what was requested.

"The link I clicked on returned a 404 error message."

See also:

SEO 101 Glossary