A Burndown Chart graphically shows how much work remains in a Sprint or release. The visualization makes it immediately apparent whether the team is on track or whether deviations are emerging. This makes the chart a simple but effective tool for transparency within the team and toward stakeholders.
The Y-axis shows remaining work, the X-axis shows time. An ideal line represents the expected progress if work is completed at a steady rate. The actual line is updated daily. If the actual line on day five of a two-week Sprint sits well above the ideal line, the team recognizes early that the planned scope is at risk. There is still time to reduce items or remove impediments, rather than discovering on the last day that half the work is missing.
The Burndown Chart goes back to Ken Schwaber and exists in two variants: the Sprint Burndown for the short-term view of a single Sprint, and the Release Burndown for the longer-term perspective. As an alternative, the Burnup Chart additionally makes scope growth visible.