The Tor Project makes a browser that allows anyone to surf the Internet anonymously. Tor stands for "the onion router" and that describes how the service works. Traffic is routed through a number of relays run across the Internet where each relay only knows the next hop (because each hop is enclosed in a cryptographic envelope), not the ultimate destination, until the traffic gets to the final exit node which connects to the website — like peeling the layers of an onion.

Think of it like a black box: traffic goes into the box, is bounced around between a random set of relays, and ultimately comes out to connect to the requested site. Anonymity is assured because anyone monitoring the network read more.