The Tor network—originally a project funded by the US Navy—is a collection of servers, some big, some smaller, spread across the world. When a user connects to the network, her internet traffic is randomly pinged between at least three of these servers, all the while covered in layers of encryption, making it near impossible for anyone monitoring the traffic to determine who is sending it or where it is going to.
It allows dissidents to communicate anonymously, citizens to bypass government censorship, and criminals to sell drugs or distribute child pornography. Tor also facilitates special sites called “hidden services,” part of the so-called dark web. These allow the owners of websites and their users to remain largely anonymous.
The final set of servers that Tor uses in this process are called “exit nodes,” because they are the points at which a user’s traffic exits the Tor network and joins the normal web that we use everyday.
Rather than being run by one company, most of these exits are set up by volunteers, or “operators.” A few organizations maintain the larger exits, a number of universities have their own, and individual activists run some too. Edward Snowden reportedly had one.