The 404 or Not Found error message is a HTTP standard response code indicating that the client was able to communicate with the server, but the server could not find what was requested.
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The web site hosting server will typically generate "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.
A 404 error should not be confused with "server not found" or similar errors, in which a connection to the destination server could not be made at all. A 404 error indicates that the requested resource may be available again in the future; however, the fact does not guarantee the same content.