Legal Definition of Source of income: The origin of income. The Internal Revenue Service frequently inquires into how and where a person came by certain income or moneys | Learn about the legal definition of source of income and its importance in taxation and financial management. Discover examples of different sources of income, such as sales revenue, wages/salary, rental income, and more. Gain valuable insights into why accurately identifying and reporting your income source is crucial for compliance, financial planning, and maximizing your earnings. Click here to understand the significance of source of income in your financial success