A bar graph is a visual representation of data that uses rectangular bars to show the quantity of different categories. Each bar's length or height corresponds to the value it represents, making it easy to compare different groups. Bar graphs can be oriented vertically or horizontally, depending on the preference of the presenter. These graphs are commonly used in various fields, such as business, education, and science, to display information clearly and effectively. They help viewers quickly understand trends, patterns, and differences among the data being presented, making them a popular choice for data visualization.