Poisson distribution expresses the probability of a given number of events of the same type (e.g., counting the number of emails received between 9:00 AM and 10:00 AM. (one event type: emails)) occurring in a fixed interval of time if these events occur with a known constant mean rate and independently of the time since the last event.
Guassian distribution is aka Normal distribution often used to examine students' scores
--Gemini & Wikipedia
