A boxplot is a graphical summary of the distribution of a sample that shows its shape, central tendency, and variability.
Boxplots can help you understand your distribution. For example, the previous boxplot could represent hold times for customer support calls. The outlier at the upper end and longer upper whisker indicate positive skewness, which is logical because at the lower end of the distribution, no hold times can be less than zero.
Boxplots are also useful for comparing several distributions. For example, a quality engineer compares the diameter of plastic pipes produced over three weeks. The following boxplot represents the results.