The Poisson distribution is different from all of the discrete distributions we have considered up until this point. Instead of counting the number of "successes" or counting the number of trials until a certain number of successes occurs, we are counting the number of occurrences of an event in a specific amount of time, area, or volume. The distribution has unique properties and is often used in environmental biology and population modeling among other applications. The end of this lesson will show the relationship between the Poisson and binomial and the Poisson and negative binomial distributions.