Probability Mass Function

Probability Mass Function-
In probability theory and statistics, a probability mass function (p.m.f) is a function that gives the probability that a discrete random variable is exactly equal ot some value. The probability mass function is often the primay means of defning a discrete probability distribution, and such functions exist for either scalar or multivariate random variables, given that the distribution is discrete.
                   A probability mass function differs from a probability density function (p.d.f) in that the latter is associated with continuous rather than discrete andom variables; the values ofthe latter are not probabilities as such: a p.d.f must be integrated over an interval to yield a probability.