Quartiles

Quartiles are position values similar to the median. Quartiles are values that divide a sample of data into four groups containing (as far as possible) equal numbers of observations.
A data set has three quartiles. References to quartiles often relate to just the outer two, the upper and the lower quartiles; the second quartile being equal to the median. The lower quartile is the data value a quarter way up through the ordered data set; the upper quartile is the data value a quarter way down through the ordered data set