- 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.
- a distribution that represents the number of events occurring randomly in a fixed time at an average rate λ; symbol P 0 (λ). For large n and small p with np = λ it approximates to the binomial distribution Bi (n,p)
