Bar charts display the data being measured and examined using bars of the same width, separated by space. Each bar represents a mutually exclusive qualitative category such as age or interest group, geographic location, time, business, organization, and so forth. The bars let you make a quick visual comparison among the categories.
One of the potential downfalls of bar charts is that they require data to be presented in discrete sets. For example, revenue in 2010, 2011, 2012, each represented as a separate bar. If your data is something more fluid that is continously changing over time, you may find it better represented by a line chart example.