The Poisson distribution is used to represent the number of occurrences or instances of a particular event (e.g., number of storms during a year, number of defects in a length of a pipe).
It is a discrete distribution containing only integer numbers. It is defined by a single value, the Expected Value of the number of occurrences or instances (which must be positive):
Note: Since this is a discrete distribution, the PDF view does not
actually display a probability density
function. Instead, it displays a probability
mass function.