English▸ noun Statistics each of four equal groups into which a population can be divided according to the distribution of values of a particular variable:
in the highest quartile, the mean age was 72.
▪ each of the three values of the random variable which divide a population into quartiles.
– ORIGIN early 16th century (in the sense ‘quadrature’ (in astronomy)): from medieval Latin quartilis, from Latin quartus ‘fourth’. The senses relating to statistics date from the late 19th century.