Skewness

Skewness is a measure of the asymmetry of a distribution. A distribution has positive skew if the assymetry is towards the positive direction, and negative skew if it is towards the negative direction. (i.e. positive skew if the positive tail is longer and negative skew if the negative tail is longer.)

Formula for skewness: (Σ_i(x_i-x_mean)³)/Nσ³

where N is the number of data points, x_i the ith data point, x_mean the mean, and σ the standard deviation.

Skewness is the third moment about the mean.