Definitions for "Quartiles"
A second quartile Q2 is a median. A first quartile Q1 is a point at or below which lies at least one-quarter of the data and at or above which lies at least three-quarters of the data. A third quartile Q3 is a point at or below which lies at least three-quarters of the data and at or above which lies at least one-quarter of the data.
Values that divide a distribution or a sample of data into four groups containing (as far as possible) equal probability or equal numbers of observations. The first or lower quartile is equivalent to the 0.25 quantile, and the third or upper quartile is the 0.75 quantile. The second quartile is the median.
The 25th, 50th and 75th percentile points. (See definition of Percentile.)