Skewness is a measure of the asymmetry of a distribution. It tells us how observations are distributed around the mean.
symmetrical distribution mode = median = mean
Positively skewed distribution
If most observations lie to the left of the mean, we say that the distribution is skewed to the right or positively skewed. This kind of distribution has a long tail on its right side.
positively skewed distribution mode < median < mean
Negatively skewed distribution
When most observations lie to the right of the mean, we say that the distribution is skewed to the left or negatively skewed. A distribution with a negative skew has a long tail on its left side.
negatively skewed distribution mean < median < mode