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. Bar graphs are commonly used in various fields, such as business, education, and science, to display information clearly. They can represent anything from sales figures to survey results, helping viewers quickly understand trends and differences among the data presented.