Middle relay

Definition
"For greater security, all Tor traffic passes through at least three relays before it reaches its destination. The first two relays are middle relays which receive traffic and pass it along to another relay. Middle relays add to the speed and robustness of the Tor network without making the owner of the relay look like the source of the traffic. Middle relays advertise their presence to the rest of the Tor network, so that any Tor user can connect to them. Even if a malicious user employs the Tor network to do something illegal, the IP address of a middle relay will not show up as the source of the traffic. That means a middle relay is generally safe to run in your home, in conjunction with other services, or on a computer with your personal files."