The quantile (this term was first used by Kendall, 1940) of a distribution
of values is a number

Similarly, the .75 quantile (also referred to as the 75th percentile or upper quartile) is a value such that 75% of the values of the variable fall below that value and is calculated accordingly. You can specify the method of computing percentiles in the Options dialog box - Analyses/Graphs: Limits tab. For more information, see Percentile Calculation Options in STATISTICA. User-specified percentiles can be calculated in Nonparametrics.

See also, Quantile-Quantile Plots and 2D Scatterplot - Quantile.