Reference desk
Glossary
Plain-language definitions for common Tor, privacy, and security terminology.
Illustration: A visual index of privacy terminology.
- Circuit
- A sequence of relays used to route traffic through the Tor network.
- Guard relay
- The first relay in a Tor circuit, selected for longer-term use.
- Middle relay
- A relay that forwards traffic between the guard and exit.
- Exit relay
- The relay that connects a Tor circuit to the public internet.
- Onion service
- A service reachable through Tor using an onion address.
- Fingerprinting
- Tracking or distinguishing a browser through combined technical characteristics.
- Threat model
- A structured description of assets, adversaries, capabilities, and risks.
- Metadata
- Information about a communication beyond its main content.
- TLS
- A protocol used to protect data in transit and authenticate connections.
- Phishing
- A deceptive attempt to obtain credentials or sensitive information.
Terms in context
- Guard relay
- The first relay in a typical Tor circuit. It can see the client’s network address, but not the final destination from the circuit alone.
- Exit relay
- The relay that connects a Tor circuit to a public-internet destination. It can observe destination metadata and unencrypted application traffic.
- Traffic correlation
- An analysis that compares timing or volume patterns at different points to infer whether flows may be related.
- Fingerprinting
- Identifying or singling out a browser through a combination of observable characteristics rather than a single stored cookie.
- Phishing
- Social engineering that attempts to trick a person into revealing credentials, codes, financial information, or taking an unsafe action.
- Onion service
- A service reachable through Tor using an onion address, with protocol features intended to conceal network location.
- Threat model
- A structured description of assets, adversaries, capabilities, exposure, and acceptable residual risk.
- End-to-end encryption
- Encryption where only the communicating endpoints are intended to possess the keys needed to read message content.
- Metadata
- Information about a communication or activity—such as time, size, participants, or routing—that may remain visible even when content is encrypted.
How to use this glossary
Security terms are context-dependent. “Anonymous” may mean that an observer cannot readily identify a person, while “pseudonymous” means activity is associated with a persistent identifier that is not necessarily a legal name. Neither term means that no information is observable. For a practical application, pair definitions with the threat-model guide and the research methodology.
Definitions are editorial summaries, not formal standards. For protocol terminology, consult the Tor specifications and NIST Glossary. Last substantive review: 11 November 2026.