The Interquartile Range (IQR) is a statistical measure that represents the range within which the middle 50% of a data set lies. It is calculated by subtracting the first quartile (Q1) from the third quartile (Q3). The first quartile is the value below which 25% of the data falls, while the third quartile is the value below which 75% of the data falls. IQR is useful for identifying outliers in a data set. Values that fall below Q1 - 1.5 * IQR or above Q3 + 1.5 * IQR are considered outliers. This method helps in understanding the spread and variability of the data, making it a valuable tool in data analysis.