This read-only string names the specific threshold package, a defined monitoring rule/metric, that a ThreshHold trap is reporting on, giving context for what's actually being measured. Admins use this to know at a glance which monitored metric triggered the trap without needing to look up a numeric threshold ID. For example, a trap with threshHoldName reading 'PortUtilization' immediately tells the admin the alert concerns port capacity rather than, say, call failure rate.