Examples of labels are `server=server1` or `team=backend`. Each alert rule can have more than one label and the complete set of labels for an alert rule is called its label set. It is this label set that identifies the alert.
For example, an alert instance might have the label set `{alertname="High CPU usage",server="server1"}` while another alert instance might have the label set `{alertname="High CPU usage",server="server2"}`. These are two separate alert instances because although their `alertname` labels are the same, their `server` labels are different.
{{<figurealt="Image shows an example of an alert instance and the labels used on the alert instance."src="/static/img/docs/alerting/unified/multi-dimensional-alert.png">}}
- [Notification policies](ref:notification-policies) and [silences](ref:silences) use labels to match alert instances and route them to contact points or stop their notifications.
- Contact points can include information from labels in notification messages.
For example, if you are monitoring temperature readings and each time series for these readings has a `sensor_id`, and a `location` label, an alert instance might have the labels `{sensor_id="1",location="NY"}`, while another alert instance might have `{sensor_id="2",location="WA"}`.
Data source query labels labels are also used to generate multiple alert instances from the same alert rule, helping to distinguish alerts from different data.
Labels prefixed with `grafana_` are reserved by Grafana for special use. To stop Grafana Alerting from adding a reserved label, you can disable it via the `disabled_labels` option in [unified_alerting.reserved_labels](/docs/grafana/<GRAFANA_VERSION>/setup-grafana/configure-grafana#unified_alertingreserved_labels) configuration.
Two alert rules cannot produce alert instances with the same labels. If two alert rules have the same labels such as `foo=bar,bar=baz` and `foo=bar,bar=baz` then one of the generated alert instances is discarded.
Grafana has a built-in Alertmanager that supports both Unicode label keys and values. If you are using an external Prometheus Alertmanager, label keys must be compatible with their [data model](https://prometheus.io/docs/concepts/data_model/#metric-names-and-labels).
This means that label keys must only contain _ASCII letters_, _numbers_, and _underscores_.
Label keys must also be matched by the regular expression `[a-zA-Z_][a-zA-Z0-9_]*`.
Any invalid characters are removed or replaced by the Grafana alerting engine before being sent to the external Alertmanager according to the following rules:
-`summary`: A short summary of what the alert has detected and why.
-`description`: A detailed description of what happened and what the alert does.
-`runbook_url`: The runbook page to guide operators managing a potential incident.
-`dashboardUId` and `panelId`: Link the alert to a dashboard and panel. These are automatically set when [creating an alert from panels](ref:create-alerts-from-panel).
