darknet
termdark webprivacyhacking
An overlay network that runs on the public internet but is reachable only with specific software, configuration, or authorization.
The word predates its reputation: a 2002 Microsoft Research paper used darknet for any private distribution network, and friend-to-friend systems like Freenet and I2P fit the definition as much as Tor does. A darknet is the underlying private network; the dark web is the websites people run on top of one. Keeping the two distinct is the difference between naming a road and naming the shops along it.
Also known as: dark net, overlay network, friend-to-friend