The Deep Web (or Invisible Web) is the set of information resources on the World Wide Web not reported by normal search engines. The term is associated with the concept of anonymity that goes with criminal intents the cannot be pursued because submerged in an inaccessible world. A parallel web that has a much wider number of information represents an invaluable resource for private companies, governments, and especially cybercrime, the Deep Web term is used by many persons. The Internet is a network of interconnected systems, are not indexed, having a size hundreds of times higher than the current web.
Source: https://thehackernews.com/2012/05/what-is-deep-web-first-trip-into-abyss.html