Bar graphs present the numbers of an item in different categories. The categories are shown on one axis, and the number of items is shown on the other axis. Bar graphs are used for comparison.
Histograms similarly use bars to compare data, but the independent variable is a continuous variable that has been “binned” or divided into categories. For example, the time of day can be broken down from 8:00 a.m. to 12:00 p.m., 12:00 p.m. to 4:00 p.m., and so on. Usually (but not always), a gap is included between the bars of a bar graph but not a histogram.