Kurtosis is a measure of the peakedness of the distribution of a real-valued
random variable. A normal distribtution has a kurtosis of zero (distributions with this kurtosis are called
mesokurtic). A distribution with positive kurtosis is called
leptokurtic, and one with negative kurtosis
platykurtic.
Kurtosis is defined as μ4 / σ4 − 3, where μ4 is the fourth moment about the mean and σ is the standard deviation.
For a set of N values the kurtosis can be calculated as Σi(xi - μ)4 / Nσ4 − 3, where xi is the ith value and μ is the mean.