APA Dictionary of Psychology

n. a value in a series of values in ascending order below which a given percentage of values lies; for example, a 50% quantile (also called a median) is the point at which 50% of the values fall below that value (and 50% above). Other types of quantile are quartiles, dividing the series into four equal-sized groups; deciles, dividing it into 10 groups; and percentiles (or centiles), dividing it into 100 groups. Also called fractile.