What is meant by a relayed conference call?

When communicating with an endpoint, if either one of the candidates (local or remote) is using a TURN server, the call is marked as relayed. callstats.io looks at the active candidate pair type, and if either is set to relay it is considered a relayed call. 

Details of the IceCandidateType is here: https://w3c.github.io/webrtc-pc/#dom-rtcicecandidatetype