Technically the Deep Web refers to the collection of all the websites and databases that search engines like Google don't or can't index, which in terms of the sheer volume of information is many times larger than the Web as we know it. But more loosely, the Deep Web is a specific branch of the Internet that's distinguished by that increasingly rare commodity: complete anonymity. Nothing you do on the Deep Web can be associated with your real-world identity, unless you choose it to be. Most people never see it, though the software you need to access it is free and takes less than three minutes to download and install. If there's a part of the grid that can be considered off the grid, it's the Deep Web.
The Deep Web has plenty of valid reasons for existing. It's a vital tool for intelligence agents, law enforcement, political dissidents and anybody who needs or wants to conduct their online affairs in private--which is, increasingly, everybody. According to a survey published in September by the Pew Internet & American Life Project, 86% of Internet users have attempted to delete or conceal their digital history, and 55% have tried to avoid being observed online by specific parties like their employers or the government.
Time (sub required)