The Dark Web often confusingly referred to as the Deep Web is the public World Wide Web content that exists on darknets, networks which overlay the public Internet and require specific software, configurations or authorization to access and are often used for illegal or criminal activity. It forms part of the Deep Web, the part of the Web not indexedby search engines. (1)
References:
1. Wikipedia page on the Dark Web: https://en.wikipedia.org/wiki/Dark_Web