Darknet

Level 3 – Deep Web

It’s the secret internet, where all the bad stuff happens and the majority of data is hidden. A dark net or darknet is an overlay network within the Internet that can only be accessed with specific software, configurations, or authorization,[1] and often uses a unique customized communication protocol. Two typical darknet types are social networks[2] (usually used for file hosting with a peer-to-peer connection),[3] and anonymity proxy networks such as Tor via an anonymized series of connections.

LINKS
https://en.wikipedia.org/wiki/Darknet