A histogram is a type of graph that shows data by using bars of different heights. The frequency of each class interval is written along the vertical axis of the graph, and it is shown by the height of the bars. On the horizontal axis of the graph, the class intervals are written down. Histograms and bar graphs may look alike, but there is a big difference between them. When making a histogram, there are no gaps between the bars because there are no gaps between class intervals. But in a bar graph, there are always equal gaps between each bar. Also, the width of the bars in a histogram can change, but the width of the bars in a bar graph stays the same.