Burn down and burn up charts are commonly used in Agile project management. They are considered a lightweight way to monitor project progress.
Both burnup and burndown charts show project progress and project velocity. That is how far the project is from completion, and how fast it is getting there.
A burn up chart shows more information than a burn down chart, notably the changes in project scope and estimation. This is useful for projects where the scope is expected to change throughout the life of the project (such as agile projects).
This presentation explains both burn down and burn up charts, how to read them, and which one to use in your projects.
TaskTrakz online project management software automatically gives you both types of charts for all of your projects, along with other progress indicators, so take a quick look at this presentation to learn how to get the most information from them at a glance.