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Glossary #

advertised bandwidth: the volume of traffic, both incoming and outgoing, that a relay is willing to sustain, as configured by the operator and claimed to be observed from recent data transfers.

bandwidth history: the volume of incoming and/or outgoing traffic that a relay claims to have handled on behalf of clients.

bridge: a server in the Tor network whose existence is non-public and which can therefore provide access for blocked clients, often in combination with pluggable transports, which registers itself with the bridge authority.

bridge authority: a special-purpose relay that maintains a list of bridges as input for external bridge distribution mechanisms (for example, BridgeDB).

circuit: a path through the Tor network built by clients starting with a bridge or relay and optionally continued by additional relays to hide the source of the circuit.

client: a node in the Tor network, typically running on behalf of one user, that routes application connections over a series of relays.

consensus: a single document compiled and voted on by the directory authorities once per hour, ensuring that all clients have the same information about the relays that make up the Tor network.

consensus weight: a value assigned to a relay that is based on bandwidth observed by the relay and bandwidth measured by the directory authorities, included in the hourly published consensus, and used by clients to select relays for their circuits.

directory authority: a special-purpose relay that maintains a list of currently-running relays and periodically publishes a consensus together with the other directory authorities.

directory mirror: a relay that provides a recent copy of directory information to clients, in order to reduce the load on directory authorities.

onion service: a service (for example, a website or instant-messaging server) that is only accessible via the Tor network.

pluggable transport: an alternative transport protocol provided by bridges and used by clients to circumvent transport-level blockings (for example, by ISPs or governments).

relay: a publicly-listed server in the Tor network that forwards traffic on behalf of clients, and that registers itself with the directory authorities.

relay flag: a special (dis-)qualification of relays for circuit positions (for example, "Guard", "Exit", "BadExit"), circuit properties (for example, "Fast", "Stable"), or roles (for example, "Authority", "HSDir"), as assigned by the directory authorities and further defined in the directory protocol specification.

rendezvous point: a relay connecting a client to an onion service, where each party builds a three-hop circuit, meeting at the rendezvous point.

server: a node in the Tor network, either a relay or a bridge, that forwards traffic on behalf of clients.