Dark Net (or Darknet) is an umbrella term describing the portions of the Internet purposefully not open to public view.
The term originally described computers on ARPANET were hidden, programmed to receive messages but not respond to or acknowledge anything, thus remaining invisible, in the dark.
The term has in later usage incorporated services such as the dark web, which is an overlay network that can be accessed only with specific software, configurations, or authorization, often using non-standard communication protocols and ports. Types of dark webs include friend-to-friend networks (usually used for file sharing with a peer-to-peer connection) and privacy networks such as Tor.
The reciprocal term for an encrypted darknet is clearnet or surface web when referring to content indexable by search engines