Final answer:
A Poisson random variable is used to describe the number of occurrences of an event over a specified interval of time or space.
Step-by-step explanation:
A discrete variable that can often be used to describe the number of occurrences of an event over a specified interval of time or space is a Poisson random variable. The Poisson probability distribution gives the probability of several events occurring in a fixed interval of time or space, if these events happen at a known average rate and independently of the time since the last event.
For example, a book editor might be interested in the number of words spelled incorrectly in a particular book and want to know the probability of a certain number of misspelled words occurring. In this case, the number of misspelled words can be modeled as a Poisson random variable.