This counts CCMs received with the Remote Defect Indication bit set, meaning the remote peer has itself detected some fault, commonly a loss-of-continuity toward one of its own other remote peers, and is using this bit to tell this MEP about it. A rising count here is this MEP learning about a problem the remote peer is experiencing elsewhere, even if the path directly between this MEP and that remote peer is otherwise fine, a subtle but important distinction when triaging where in a multi-point service a fault actually originated.