Infrastructure
What is Tor?
A free network that hides a user's location by routing traffic through three volunteer relays, and that hosts .onion sites.
Tor, originally "The Onion Router", routes traffic through three volunteer-run relays with layered encryption, so no single relay knows both who the user is and where they are going. The Tor Browser makes this usable for ordinary browsing.
Tor also hosts onion services, websites reachable only inside the network. It is used by journalists, activists and privacy-minded users, and by criminals running markets and leak sites. Because exit relays are public, websites can tell when a visitor is using Tor.