DefinitionPoisson Distribution is a probability distribution which expresses the possibility of a given number of events happen in a fixed interval of time or space. In this type of distribution, the events are independent and the rate, denoted “λ”, is also constant. For example, it is the type of distribution that can be used to best represent the number of hourly e-mails received assuming that the e-mails are being received at random times and also that the independent events are not received.