It's just a 404 Error.

The 404 or Not Found error message is an HTTP standard response code
indicating that the client was able to communicate with a given server, but the
server could not find what was requested.

The web site hosting server will typically generate a "404 Not Found" web page
when a user attempts to follow a broken or dead link; hence the 404 error is one of
the most recognizable errors users can find on the web.
Server Level 404 (html)