Skewness is the degree of asymmetry or departure from the symmetry of the distribution of a real-valued random variable. If the frequency curve of distribution has a longer tail to the right of the central maximum than to the left, the distribution is said to be skewed to the right or to have positively skewed. In a positively skewed distribution, the mean is greater than the median, and the median is greater than the mode i.e. Mean > Median > Mode.
If the frequency curve has a longer tail to the left of the central maximum than to the right, the distribution is said to be skewed to the left or to be negatively skewed. In a negatively skewed distribution, the mode is greater than the median and the median is greater than the mean i.e. Mode > Median > Mean.