In descriptive statistics, the range is the length of the smallest interval which contains all the data. It is calculated by subtracting the smallest observations from the greatest and provides an indication of statistical dispersion.
It is measured in the same units as the data. Since it only depends on two of the observations, it is a poor and unrobust measure of dispersion except when the sample size is large.
For a population, the range is more than twice the standard deviation.
The midrange point, i.e. the point halfway between the two extremes, is an indicator of the central tendency of the data. Again it is not particularly robust for small samples.