The Label Burndown Chart is a graphical representation of remaining unfinished work (Stories) with that Label. In a Label, the Burndown Chart is located in the Reports tab.
The Burndown Chart is displayed in either Story Count or Points. Configure this setting in Settings > Estimate Scale.
The Burndown Chart displays the unfinished Story Count or Points on a given day.
The start date of the Burndown Chart is the first date that a Story with that Label was completed.
The end date of the Burndown Chart is the most recent date that a Story with that Label was completed.