The deep Web is the part of the Internet that is inaccessible to conventional search engine s, and consequently, to most users. According to researcher Marcus P. Zillman of DeepWebResearch.info, as of January 2006, the deep Web contained somewhere in the vicinity of 900 billion pages of information. In contrast, Google, the largest search engine, had indexed just 25 billion pages.
Deep Web content includes information in private databases that are accessible over the Internet but not intended to be crawled by search engines. For example, some universities, government agencies and other organizations maintain databases of information that were not created for general public access. Other sites may restrict database access to members or subscribers.
The term, "deep Web," was coined by BrightPlanet, an Internet search technology company that specializes in searching deep Web content. In their 2001 white paper, 'The Deep Web: Surfacing Hidden Value,' BrightPlanet noted that the deep Web was growing much more quickly than the surface Web and that the quality of the content within it was significantly higher than the vast majority of surface Web content. Although some of the content is not open to the general public, BrightPlanet estimates that 95% of the deep Web can be accessed through specialized search.