Probability Distributions (PMF, CDF, PDF)

The Probability Mass Function or PMF is used to calculate the probability that a DISCRETE random variable will take an EXACT given value.
The cumulative distribution function or CDF is used to calculate the probability that a random variable is less than or equal to a certain value.
The Probability Density Function or PDF is used to calculate the probability that a value of a random variable fall between a certain range of values.