Correlation, in statistics, refers to relationship between any two, or more variables viz. height and weight, rainfall and yield, price and demand, income and expenditure, wages and price index, production and employment etc. Two variables are said to be correlated if with a change in the value of one variable there arises a change in the value of another variable.On the other hand, if a change in the value of one variable does not bring any change in the value of another variable, the two variable are said to have no relation with each other. Thus, if with a change in the price of a commodity the demand for that commodity changes, we would say that the variable price, and the demand for that commodity changes, we would say that the variables price, and the demand are related with each other. But there is no correlation between the heights of certain persons and the price of certain commodity because, any change in the height level of certain persons. In statistics, the study of correlation between any two, or more variables becomes necessary with a view to estimating the values of one variable in the light of the values of another variable. In the field of business, and economics demand etc. becomes usual, and indispensable without which a businessman can not succeed in his business, and an economist can not draw his relevant laws if the two concerned variables have any relationship with each other. For this, the study of correlation between any two variables becomes necessary.