The relationship between the variable input and output, keeping all other inputs fixed, is known as the Total Product of the variable input. It is also known as the summation of the total output produced by a firm by the employment of a specific input. The average product may be defined as output produced per unit of the variable input. It is the ratio of the total product (TP) to the total units of labour employed.The marginal product of input may be defined as the change in output per unit of change in input, keeping all other input parameters constant.