When people talk about Tor, they may be talking about one or more of the following Tor technologies:
The Tor protocol: The official system of rules governing the operations of Core Tor, the Tor network, and Onion Services. The Tor protocol is publically accessible and readily criticized and updated.
Core Tor: A software application that uses strong encryption and careful routing designed to hide network identifying information of a computer from other Internet resources. Core Tor is a free software technology that can be built into many Internet products.
The Tor network: The global network of volunteer administrators that make Tor technologies so powerful and successful. Volunteers run “relays” that route Core Tor and Onion Services traffic on the Internet. Each of the 7,000+ volunteer relay administrators can be one of three “hops” that Tor users rely on when using Tor technologies. When Tor technologies are used, traffic moves from relay to relay, each hop preventing network origination information from being shared with the destination. Relay diversity is important because of the need for distributed trust.
Tor Browser: A customized Firefox web browser that has been modified to minimize identity exposure to web sites and advertising networks. One critical feature of Tor Browser is that all traffic from Tor Browser is routed through the Tor network.
Onion Services: The dot-onion (.onion) is a special “top level domain”, similar to dot-com (.com), but is only recognized by Tor technologies. Onion Services are diverse and can be used by many types of Internet tools. For example, in Tor Browser, connecting to a dot-onion web address allows a server to share content anonymously with a user, and allows a user to connect anonymously to a server. Onion Services are also used by instant messaging tools like Ricochet which allows people to anonymously chat with each other.
Pluggable Transports: It is commonplace for governments or corporations to limit, censor, or surveil their Internet users. Pluggable Transports are free software technologies that allow Tor technologies to bypass censorship by changing how the Internet traffic appears to these restrictive organizations.