Introduction to Probability Distribution 
By  theoretical distribution we mean  a frequency distribution  which  is obtained  in relation to a random  variable by some  mathematical  model. The types  of such  a distribution are:
a.Binomial  distribution
b.Poisson distribution
c.Normal distribution etc.
Such  distribution  are otherwise  called  probability  distribution  or expected frequency  distribution  of a random  variable. Which  are built  up on the  basis  of previous  experience  or some  theoretical  considerations.