

This layered concept is called "Onion Routing". Since the data is encrypted multiple times, the data is often compared to an onion with many layers (hence the name). Then, the next relay decrypts another layer and sends the data to the next relay until the data reaches the client or server. Each relay decrypts the data once to get information as to where to send the data next. When a Tor client connects to a server, a random path between the client and server is created among the Tor relays. Tor networks are made up of "Tor Relays".

Tor is an acronym for "The Onion Router". The browser is available for all systems including Windows, Linux (and Android), OS X, iOS, and various Unixoid systems.

Tor is open-source freeware written is C.
