Random error term refers to the description term of random error in mathematical expression. In the population regression parameter PRF, we express the deviation of individual Yi around its expected value as: Ui=Yi-E(Y|Xi), where the deviation Ui is an unobservable random variable, which can be positive or negative, and it is called random interference or random error term in technical terms. Therefore, the interference term replaces all the variables ignored in the model and affects Y together.