Kurtosis measures the peakedness of a distribution and the probability of extreme outcomes (thickness of tails):

• Excess kurtosis is measured relative to a normal distribution, which has a kurtosis of 3.
• Positive values of excess kurtosis indicate a distribution that is leptokurtic (fat tails, more peaked), so the probability of extreme outcomes is greater than for a normal distribution.
• Negative values of excess kurtosis indicate a platykurtic distribution (thin tails, less peaked).