The procedure of estimating the missing value of y for a given value of x, where x is within the limits x_{0} and x_{n} we use Interpolation. Here “Interpolation is a procedure of estimating the unknown value of dependent variable for a given value of independent variable which is within the limits or the range of the independent variable”.

But if the value of y is to be estimated for a value of x which is outside the limits x, and x, then procedure Extrapolation is used. Here “Extrapolation is a procedure of estimating the unknown value of dependent variable for a given value of independent variable which is outside the limits or the range of the independent variable”.