Task burn-down and burn-up charts are two types of the so called "burn" chart. Both graphs are great for measuring progress and performance of certain work (generally projects).
Task Burn-down Chart is a graphical representation of a project to show how much work remains on the project and whether the team will hit the project deadline. The graph has 1) the vertical axis that measures the work remaining and 2) the horizontal axis that marks iterations. The chart is built upon simple tasks and activities that compose the job. As every next task or activity is completed, a respective mark is added to the chart, and so it becomes easier to see whether the project moves forward and whether it hits the target date. All marks are combined into the progress line cruising to zero.
Task Burn-up Chart displays how much work is done. The bottom line of the chart shows the work done (expressed as number of task iterations) and the top line depicts the total scope (expressed as work performance). As tasks are done, new respective marks are added to the graph. If scope gets changed, the target date gets either extended or shortened. Dependency between iterations and scope changes is depicted by a horizontal progress line that rises up.