(It's called 'onion' routing because it has multiple layers, like an onion.) Traffic passes through random servers (or nodes) kept running by, well, anybody. Tor uses layers of encryption to keep your traffic secure.

If your primary concern online is to try and stay anonymous, this is something you’d turn to. In fact, it was originally created to keep US intelligence communications safe. Although the Dark Web has a reputation for being a place where criminal activity takes place there is nothing intrinsically bad or criminal about Tor. The network of websites and services that are only accessible using Tor is often referred to as 'The Dark Web' or, more correctly, 'The Dark Net'. It’s designed to block tracking and eavesdropping, resist fingerprinting (where services tie your browser and device information to an identity), and to hide the location of the people using it.

Tor (The Onion Router) is free software used to keep your online communications safe and secure from outside observers.

Antivirus to use with tor web browser