Difference between trigger threshold and metric_trigger threshold in terraform

Question

I was adding metric alerts to monitor a web api hosted in AKS and was looking azurerm_monitor_scheduled_query_rules_alert here. I could not tell the difference between the two thresholds. I am confused about the purpose and where each one applies ?

trigger {
    operator  = "GreaterThan"
    threshold = 3
    metric_trigger {
      operator            = "GreaterThan"
      threshold           = 1
      metric_trigger_type = "Total"
      metric_column       = "operation_Name"
    }
  }