Poisson distribution
noun
Pois·son distribution pwä-ˈsōⁿ- 
: 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 {latex}f(x) = \\frac{e^{-\\mu}\\mu^{x}}{{x!}}{/latex} where μ is the mean and x takes on nonnegative integral values
Word History
Etymology
Siméon D. Poisson †1840 French mathematician
First Known Use
1922, in the meaning defined above