QUARTILES
The quartile is a measure of location for one quantitative variable.
The first quartile ( Q1 ) is the point in the data where 1/4 of the values
are smaller than Q1 and 3/4 of the values are greater than Q1. The third
quartile ( Q3 ) is the point in the data where 3/4 of the values are smaller
than Q3 and 1/4 of the values are greater than Q3. The second quartile
( Q2 ) is better known as the median.
N-R Glossary Looking
at Data