A measure of the lack of symmetry of a distribution. The formula for skewness is shown here, where Y-Bar is the mean, s is the standard deviation and N is the number of data points in the sample.A positive value for skewness indicates that the data are skewed right, meaning that the right tail is "heavier", pulling the mean to the right of the median. Conversely, a negative value for skewness indicates that the data are skewed left.Symmetric distributions (such as the Normal distribution) will have a skewness value close to zero.
Mode = Mo, Median = Md, Mean = Mn
NIST Statistics Handbook: Measures of Skewness and Kurtosis - http://www.itl.nist.gov/div898/handbook/eda/section3/eda35b.htm