Kurtosis is a statistical measure of the tails of a frequency distribution when compared with a normal distribution. Numerically the kurtosis is the fourth standardized moment (a4). Kurtosis can also be expressed using the second and third central moments (m2 and m3).
The kurtosis for a standard normal distribution is 3. For this reason, the following definition of kurtosis (often referred to as "excess kurtosis") can also be used.
The excess kurtosis can be positive or negative.
