Skewness is a statistical measure that describes the asymmetry of a data distribution. When a distribution is skewed, it means that the data points are not evenly distributed around the mean. A positive skew indicates that the tail on the right side is longer or fatter, while a negative skew indicates that the tail on the left side is longer or fatter. Understanding skewness helps in analyzing data sets, as it can affect the results of statistical tests. For example, in a normal distribution, skewness is zero, indicating a symmetrical shape. Identifying skewness can guide decisions on data transformation or the choice of statistical methods.