Burndown is the estimated amount of work that remains to be done in an iteration, compared with the work that was originally estimated.
TeamForge generates a handy chart that helps you see your burndown rate. You can use the trend line shown in your burndown chart to do some useful things:
The information you derive from your burndown chart will help revise the product scope, make accurate planning decisions, and refine implementation details.
In general, a burndown chart trends downward until it reaches zero. In practice, some events can reverse the downward trend of your burndown chart. For example, development work frequently uncovers a greater scope for a user story than was initially estimated. As a result, you'll revise your estimate of remaining work on that story, and your burndown figure may be pushed upwards.