POIS - Poisson distribution
The Poisson distribution is a discrete distribution. In the Poisson process, the average rate of success over time is known. The value of the resulting variable has non-negative integer values.
The probability of a single success within a time interval is proportional to the length of the interval. The probability is also independent of the probability that is outside of the interval. If the interval gets shorter, the probability of more than one success goes toward zero.
The Poisson distribution has one parameter, the mean parameter.