A generic term for any fraction that divides a collection of observations arranged in order of magnitude into two specific parts. Thus, the upper quartile is the quantile that separates the upper one-quarter from the lower three-quarters of the observations. See also percentile, decile.
(of a variable) The th quantile is a value such that a fraction of the individuals do not exceed that value, and a fraction 1- have at least that value. (cf. : percentile) The 1/4, 1/2, and 3/4 quantiles are generally called lower quartile, median, and upper quartile, respectively. (of a distribution) The th (lower) quantile is a value such that the probability of being less than that value is no more than and the probabiity of being greater than it is no more than 1-. The th upper quantile is the same as the 1- th lower quantile. Quantiles are also (loosely) called perentage points, particularly when used in hypothesis testing.