In statistics, quartiles are a type of quantiles which divide the number of data points into four parts, or quarters, of more-or-less equal size. The data must be ordered from smallest to largest to compute quartiles; as such, quartiles are a form of order statistic. The three quartiles, resulting in four data divisions, are as follows:

• The first quartile (Q₁) is defined as the 25th percentile where lowest 25% data is below this point. It is also known as the lower quartile.
• The second quartile (Q₂) is the median of a data set; thus 50% of the data lies below this point.
• The third quartile (Q₃) is the 75th percentile where lowest 75% data is below this point. It is known as the upper quartile, as 75% of the data lies below this point.