The Iteration Burndown Chart is a graphical representation of remaining unfinished work in that Iteration. In an Iteration, the Burndown Chart is located in the Reports tab of the Iterations Detail Page.
The Burndown Chart can be displayed in either Story Count or Points. Configure this setting in Settings > Estimate Scale.
The Burndown Chart displays the unfinished Story Count or Points in the Iteration on a given day.
The start date and end date of the Iteration Burndown Chart is the start date and end date of the Iteration, respectively.
The Burndown Chart displays an estimate of when all Stories or Points will be completed.