The Deep Web (also called the Deepnet, the Invisible Web, the Undernet or the hidden Web) is World Wide Web content that is not part of the Surface Web, which is indexed by standard search engines. It should not be confused with the dark Internet, the computers that can no longer be reached via Internet, or with a Darknet distributed filesharing network, which could be classified as a smaller part of the Deep Web. Mike Bergman, founder of BrightPlanet and credited with coining the phrase, said that searching on the Internet today can be compared to dragging a net across the surface of the ocean: a great deal may be caught in the net, but there is a wealth of information that is deep and therefore missed.
Most of the Web’s information is buried far down on dynamically generated sites, and standard search engines do not find it. Traditional search engines cannot “see” or retrieve content in the deep Web, those pages do not exist until they are created dynamically as the result of a specific search. As of 2001, the deep Web was several orders of magnitude larger than the surface Web.
Hackers utilize malicious techniques to hijack private routers to either divert traffic or mask illegal activity. Through use of these private routers, a deep Web can form and be used to conduct all manner of misconduct on the Internet. The deep Web received attention in 2001 when many security organizations, including Arbor Networks, identified rogue dark networks as a potential farm for denial-of-service attacks and other illegal activity. The Deep Web means two things. In some cases it’s used to refer to the part of the web that isn’t reached by search engines.
Second, and more relevant to this case, it refers to a series of web sites that are only accessible through the Tor anonymity service. Tor is software that routes your web connections through a number of other web servers – possibly around the world – in order to hide the source and destination of the connection. Typically you use Tor to access normal web sites, with the guarantee that the website can’t trace you. However Tor also allows the destination web site to be in an anonymous location, also known as a “Tor Hidden Service”.
Thus in the second usage, the Deep Web is the name people give to the part of the web that’s made up only of Tor hidden services. This is a pretty strange bunch of sites, including Silk Road (closed from FBI) and some other legal and illegal services. It’s an interesting place.
Estimates based on extrapolations from a study done at University of California, Berkeley in 2001, speculate that the deep Web consists of about 7,500 terabytes. More accurate estimates are available for the number of resources in the deep Web: research of He et al. detected around 300,000 deep web sites in the entire Web in 2004, and, according to Shestakov, around 14,000 deep web sites existed in the Russian part of the Web in 2006. The GeekBlogTv explain you in the short video below some more info about the “Deep Web”