a limiting form of the binomial probability distribution for small values of the probability of success and for large numbers of trials: particularly useful in industrial quality-control work and in radiation and bacteriological problems.

British Dictionary definitions for poisson distribution

Poisson distribution

/ (ˈpwɑːsən) /

noun

statisticsa distribution that represents the number of events occurring randomly in a fixed time at an average rate λ; symbol P0 (λ). For large n and small p with np = λ it approximates to the binomial distribution Bi (n,p)

A probability distribution which arises when counting the number of occurrences of a rare event in a long series of trials. It is named after its discoverer, French mathematician and physicist Siméon Denis Poisson (1781-1840).