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.
Darknet is the older and broader term, originally describing any network that is not publicly routed: private overlays, closed file-sharing networks, and in some usages the unallocated address space that receives only unsolicited traffic.
That last usage is worth separating because it is genuinely different and useful. A darknet in the network-telescope sense is a block of routed but unused addresses, and everything arriving there is by definition unsolicited: scanning, worm propagation, backscatter from spoofed attacks. Watching one is a cheap and effective way to measure internet-wide malicious activity, and it has nothing to do with the dark web the term is usually confused with.
Also known as: dark net, overlay network, friend-to-friend