Tor
termprivacysecuritydark web
Stands for: The Onion Router
An anonymity network that routes traffic through three volunteer relays, each peeling one layer of encryption, so no single relay knows both ends.
Onion routing came out of the US Naval Research Laboratory in the 1990s, and the paradox is the design: a network used only by spies would identify its users as spies, so it had to be public and popular to work at all. The three-hop circuit splits knowledge (the guard sees you, the exit sees your destination, neither sees both), and .onion addresses are public keys rather than registered names, so they authenticate the server by construction. Worth correcting the usual assumption: only a small single-digit share of Tor traffic reaches onion services, and the rest simply exits to the ordinary web.
Tor routes traffic through several relays with layered encryption, so no single relay knows both who sent a message and where it is going. That is its entire guarantee, and it is a strong one within its threat model.
What it does not defend against is the endpoints and the correlation. A user who logs into an identifying account, or runs a browser configured differently from everyone else's, deanonymizes themselves regardless of the network. An adversary observing both ends of a circuit can correlate timing and volume, which is why Tor's own documentation is explicit that a global passive adversary is outside its threat model. Using it well is a discipline rather than an installation.
Also known as: The Onion Router, Tor Browser, onion service, hidden service, .onion