Tor is free software for enabling anonymous communication. The name is derived from an acronym for the original software project name “The Onion Router”.
Tor directs Internet traffic through a free, worldwide, volunteer overlay network consisting of more than seven thousand relays to conceal a user’s location and usage from anyone conducting network surveillance or traffic analysis. Using Tor makes it more difficult to trace Internet activity to the user: this includes “visits to Web sites, online posts, instant messages, and other communication forms”.
Tor’s intended use is to protect the personal privacy of its users, as well as their freedom and ability to conduct confidential communication by keeping their Internet activities from being monitored.
Tor does not prevent an online service from determining when it is being accessed through Tor. Tor protects a user’s privacy, but does not hide the fact that someone is using Tor.
Some websites restrict allowances through Tor. For example, the MediaWiki TorBlock extension automatically restricts edits made through Tor, although Wikipedia allows some limited editing in exceptional circumstances.