Pronunciation: pwä- ' s ō n -
Function: noun
Etymology: Siméon D. Poisson † 1840 French mathematician
Date: 1922
: a probability density function that is often used as a mathematical model of the number of outcomes obtained in a suitable interval of time and space, that has its mean equal to its variance, that is used as an approximation to the binomial distribution, and that has the form f ( x ) = e - µ µ x / x ! where µ is the mean and x takes on nonnegative integral values