quartile

In descriptive statistics, a quartile is any of the three values which divide the sorted data set into four equal parts, so that each part represents 1/4th of the sampled population.Thus:first quartile (designated Q1) = lower quartile = cuts off lowest 25% of data = 25th percentilesecond quartile (designated Q2) = median = cuts data set in half = 50th percentilethird quartile (designated Q3) = upper quartile = cuts off highest 25% of data, or lowest 75% = 75th percentileThe difference between the upper and lower quartiles is called the interquartile range.
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Noun
1. (statistics) any of three points that divide an ordered distribution into four parts each containing one quarter of the scores
(hypernym) mark, grade, score
(classification) statistics

n. quartile

(n.)
Same as Quadrate.
  

The lower and upper quartiles (this term was first used by Galton, 1882; also referred to as the .25 and .75 quantiles ) are the 25th and 75th percentiles of the distribution (respectively). The 25th percentile of a variable is a value such that 25% of the values of the variable fall below that value.
Similarly, the 75th percentile is a value such that 75% of the values of the variable fall below that value and is calculated accordingly.