From fucking Tor Project themselves:
https://www.torproject.org/docs/faq#WhatIsTor
The name "Tor" can refer to several different components.
The
Tor software is a program you can run on your computer that helps keep you safe on the Internet. Tor protects you by bouncing your communications around a distributed network of relays run by volunteers all around the world: it prevents somebody watching your Internet connection from learning what sites you visit, and it prevents the sites you visit from learning your physical location.
