Google, the largest search database on the planet, currently has around eight
billion web pages indexed. That's a lot of information. But it's nothing
compared to what else is out there. Google can only index the visible web, or
searchable web. But the invisible
web, or deep web, is estimated to be 500
times bigger than the searchable web. The invisible web comprises databases
and results of specialty search engines that the popular search engines simply
are not able to index.