This read-only INTEGER is a trap varbind that, per its source description, uniquely identifies this specific notification event. Admins use this ID together with the request ID when running the resdata utility (with the -n option) to retrieve monitor-specific data tied to this exact notification instance, as opposed to the broader monitoring request. For example, running "resdata -r <resource name> -R <request id> -n <notify id> -m" would pull the monitor data specific to this one notification event.