Definition
A Tor bridge is an entry relay into the Tor anonymity network whose IP address is deliberately kept off the public relay list. Because censors commonly enumerate and block the published addresses of ordinary Tor guard relays, an unlisted bridge gives a sovereign user a connection point the blocker does not already know about. For the educational purpose of restoring access to one's own lawful, anonymous communication, bridges are the first line of defense when a network operator filters Tor by address.
Why unlisted matters
Censors typically block Tor in two ways: by blacklisting the IP addresses of known relays, and by inspecting traffic for the Tor protocol signature. A bridge defeats the first method. Volunteers run bridges and distribute their addresses through rationed, hard-to-scrape channels (a web request, email, or built-in defaults), so an adversary cannot simply download a master list and ban every entry at once.
Bridges plus obfuscation
An address that is merely unlisted still looks like Tor on the wire, so a determined censor using packet inspection can fingerprint and block it. For this reason bridges are most effective when combined with a traffic-disguising layer, so that the connection neither appears on a blocklist nor matches a recognizable protocol pattern. This layered approach is the foundation of practical circumvention for self-hosted, privacy-respecting setups.
For related concepts on how bridge traffic is disguised, see the pluggable transport and obfs4 glossary entries.
In Simple Terms
A Tor bridge is an entry relay into the Tor anonymity network whose IP address is deliberately kept off the public relay list. Because censors…