A theoretical distribution that is a good approximation to the binomial distribution when the probability is small and the number of trials is large WordNet 3.0 & Open English WordNet

In probability theory and statistics, the Poisson distribution is a discrete probability distribution that expresses the probability of a given number of events occurring in a fixed interval of time or space if these events occur with a known constant mean rate and independently of the time since the last event. Wikipedia

The use of that name for this distribution originated in the book The Law of Small Numbers Wikipedia Disambiguation

Discrete probability distribution Wikidata

Any of a class of discrete probability distributions that express the probability of a given number of events occurring in a fixed time interval, where the events occur independently and at a constant average rate; describable as a limit case of either binomial or negative binomial distributions. Wiktionary

Probability distribution. Wiktionary (translation)