Skewness is a statistical measure that describes the degree of asymmetry in a distribution of data. It is a measure of the deviation of a distribution from symmetry around its mean. A distribution is said to be skewed if it is not symmetric around its mean.

There are two types of skewness: positive skewness and negative skewness. Positive skewness occurs when the tail of the distribution is longer on the right side than on the left side, while negative skewness occurs when the tail of the distribution is longer on the left side than on the right side.

Skewness is usually measured using a statistic called the skewness coefficient, which is a measure of the degree of asymmetry of a distribution. The skewness coefficient can take on positive or negative values, depending on whether the distribution is positively or negatively skewed. A skewness coefficient of zero indicates that the distribution is perfectly symmetrical.