..despite Google’s web prowess, it and other search engines have a very limited view of what’s out there. (Some researchers say that search engines only show about 1% of what’s actually available online!).
Deep Web, Dark Web, Hidden Web… synonyms for the data locked away beyond the reach of search engine crawlers. You have to find the site and dig in using the local tools. Despite a bit of fear mongering, this is a clever article with an interesting infographic.