A five-number summary of a data set consists of the following five values.

1. Minimum value
2. First quartile $Q_1$
3. Median, or second quartile $Q_2$
4. Third quartile $Q_3$
5. Maximum value

These values provide a summary of the central tendency and spread of the data set. The five-number summary is useful for understanding the variability in a data set. When the data set is written in numerical order, the median divides the data set into two halves. The median of the lower half is the first quartile $Q_1$ and the median of the upper half is the third quartile $Q_3.$ The five-number summary describes the distribution of data values.