This is rmtErrDescr, the human-readable text explaining the remote error recorded in rmtErrCode for this domain's identity-sync FSM. When an identity sync with the peer fabric interconnect or UCS Central fails, this is the field an admin actually reads in the fault/event log to understand the failure in plain language rather than decoding a bare numeric code. It might read something like 'connection to peer fabric interconnect timed out' when that specific failure occurs.