A quartile is a statistical measure that divides a dataset into four equal parts, representing three points that divide the data set into four quarters. These points are known as the first quartile (Q1), the second quartile (Q2, which is the same as the median), and the third quartile (Q3). The first quartile (Q1) marks the boundary below which 25% of the data points lie, while the third quartile (Q3) marks the boundary below which 75% of the data points lie. Quartiles are used to understand the distribution, variability, and relative positions of values within a dataset, particularly in descriptive statistics and box plots.