This read-only OCTET STRING is a trap varbind that, per its source description, names the kind of notification being sent: Poll (fired at every monitoring interval), Change (fired when the value changes), Normal (threshold condition not true), Problem (threshold condition true), or Error (the monitor couldn't determine the resource's value). Admins use this string to distinguish, for example, a routine interval poll from an actual threshold breach when processing incoming EMS traps. For example, an EventType of "Error" tells an admin the alert isn't about the resource's value at all, but about the monitor itself failing to read it.