The “invisible” web or “deep web” (sometimes also called the “dark web”) refers to the huge repository of online content, such as documents in databases or data on password-protected websites that search engine crawlers cannot reach.

It is estimated that the invisible web is at least 500 times the size of the visible web. Commercial search engines index only the the visible web.

Employers have started to perform deep web searches on candidates. If you are only using a search engine to search for your name online, you may not be seeing all of the information that is out there about you.

Found a few more.

I do wonder how much bigger the Dark Web is.