Surplus income refers to the amount of money that an individual or household has left over after all necessary expenses have been paid. It is essentially the difference between total income and total expenditure, with any remaining balance being classified as surplus income. This term can also be used in a broader sense to refer to the excess production capacity of a country or industry beyond what is needed to meet current demand. In economics, it is often seen as an indicator of economic health, with higher levels of surplus income suggesting greater financial stability and prosperity for individuals and businesses alike.