Skewness is a measure of assymetry of a distribution. A positive skew indicates that the right tail is longer and the mass of the distribution is concentrated on the left. A negative skew indicates that the left tail is longer and the mass of the distribution is concentrated on the right.
The formula for unbiased skewness is


= data set
= number of data values in 
= mean of the data set

= standard deviation of the data set
The formula for biased skewness is
