Named after Siméon-Denis Poisson (1781-1840), it is a skewed probability distribution with a long tail representing the number of randomly occurring events with a constant mean rate in a specified time interval. Its most frequent use is to model the random occurrence of infrequent events that have a fixed probability of occurrence. It has also been used to model developmental changes in the temporal organisation of infant nutritive sucking and turn-taking during face-to-face interaction in older infants.