deep web

The deep web refers to the vast repository of information that search engines and directories don't have direct access to, namely databases. It is true that information from the deep Web is "buried so deep" that it doesn't show up in most organic search results, and it is estimated that the deep Web is 500 times larger than the visible web (or surface web).

The dark web forms a small part of the deep web, the part of the web not indexed by web search engines, although sometimes the term deep web is mistakenly used to refer specifically to the dark web. The dark Web is also synonymous with hackers, online predators, pornography, and other types of sinister and illegal behaviors.

Basically the reason why such a large portion of the web is not indexed by search engines is because it consists of dynamic pages within database-driven Web sites. Deep web URLs are identifiable in that they are very long and contain symbols, such as question marks or percentage signs. If you are doing an online search and can't find what you're looking for, try using a Web site's site search to delve deeper.