Source : WordNet®

Poisson distribution
     n : a theoretical distribution that is a good approximation to
         the binomial distribution when the probability is small
         and the number of trials is large

Source : Free On-Line Dictionary of Computing

Poisson distribution
     
         A {probability distribution} used to describe
        the occurrence of unlikely events in a large number of
        independent trials.
     
        Poisson distributions are often used in building simulated
        user loads.
     
        [Formula?]
     
        (2003-03-18)