is about
data item
data set
probability distribution
quantile
Alejandra Gonzalez-Beltran
Evans, M.; Hastings, N.; and Peacock, B. Statistical Distributions, 3rd ed. New York: Wiley, 2000.
Orlaith Burke
Philippe Rocca-Serra
a quantile is a data item which corresponds to specific elements x in the range of a variate X.
the k-th n-tile P_k is that value of x, say x_k, which corresponds to a cumulative frequency of Nk/n (Kenney and Keeping 1962). If n=4, the quantity is called a quartile, and if n=100, it is called a percentile.
http://mathworld.wolfram.com/Quantile.html
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