Google does indeed call these soft 404s…Soft 404s are a pet peeve of mine.
They are very common, many of the sites I have access to the Google Search Console data for have them.
But they shouldn’t.
If a server can’t return the content the client is requesting, it should inform the client (by returning an error message via HTTP header, not returning a ‘200’ series “success” header).
According to Google, 404s won’t harm your rankings
Regardless, here’s the code from my “default” 404 page:
<h1>Page Not Found</h1> <p>Something isn't right here, the URL you requested isn't available.</p> <p>Go to the <a href="https://webmasters.stackexchange.com/">home page</a>.</p> <p>Try the <a href="http://webmasters.stackexchange.com/sitemap/">sitemap</a>.</p> <p>Maybe the <a href="https://web.archive.org/">Internet Archive's Wayback Machine</a> has a copy of that page…</p> <div id="wb404"></div> <script src="https://archive.org/web/wb404.js"></script> <p>Or maybe Google can help…</p> <script> var GOOG_FIXURL_LANG = (navigator.language || '').slice(0,2),GOOG_FIXURL_SITE = location.host; </script> <script src="https://linkhelp.clients.google.com/tbproxy/lh/wm/fixurl.js"></script>
It’s a bit of overkill but I offer users:
1.) an explanation that the page they requested in unavailable
2.) a link to the home page
3.) a link to the HTML sitemap
4.) a script from archive.org that attempts to show old versions of the page from The Wayback Machine
5.) a Google script that attempts to guess what they were requesting