"The Cloaked Web"- hidden from regular search engines.
Ever wonder if Google finds everything? Read this article by Paul Gil for a primer on what percent of the internet's 300+ billion webpages show up in a search.
"Many untrained users have the naive expectation that they can locate anything on the world wide web by using Google or Yahoo or Ask.com. No, as powerful as these search engines are, they do not index everything on the world wide web. In fact, search engines index less than 10% of the entire web! That remaining 90% is called the "Invisible Web", or in other words, "The Cloaked Web" or "The Deep Web". This is the massive content that is publicly available, but hidden from regular search engines."