Wouldn’t it be nice to earn money while not working? That money is called residual, or recurring, income. It's what can happen after you put a lot of time, effort and sometimes money into a job to continue to get paid for the work months or years after it's done. (Salary jobs are part of linear income. This income is directly related to the number of hours you work. If you work 40 hours, you get paid for 40 hours of work.) Once you set up your business to earn residual income, you continue to make money while doing other things – maybe even starting a new business to generate more residual income!
In equity valuation, residual income represents an economic earnings stream and valuation method for estimating the intrinsic value of a company's common stock. The residual income valuation model values a company as the sum of book value and the present value of expected future residual income. Residual income attempts to measure economic profit, which is the profit remaining after the deduction of opportunity costs for all sources of capital.