What is the fundamental difference between a 'hard 404' and a 'soft 404' error, and how should each be addressed?

The fundamental difference between a 'hard 404' and a 'soft 404' error lies in the server's response and how search engines interpret it. A 'hard 404' error occurs when a web server correctly returns a 404 HTTP status code, indicating that the requested resource (page or file) is not found. This is the proper way to signal that a page doesn't exist. A 'soft 404'....