Active income, on the other hand, involves earning money in exchange for a service. It could be a salary, an hourly wage, commissions, or tips. It’s essentially a trade of your time for a fixed dollar amount. Most people choose to live this way, and there’s nothing inherently wrong with that, as long as you understand that there will be a limit to how much money you can realistically earn.
That income is considered residual income because as long as the apartment is rented and the rent is collected, the income is earned without additional effort. The effort came when the property was purchased and a tenant was found. Each month after that, the money automatically is paid without buying the apartment again or finding the same tenant each month.

Residual income is the best model for money generation. Once you master and build up one avenue, you can devote your time and money into another avenue. Eventually you start reaping the benefits of multiple residual income avenues. Enabling you to have complete financial and time freedom. I recommend to all people to build these types of asset models as they can greatly improve their life.
Well written piece, but I question the core premise. Why the fascination with maximizing “income” (passive or otherwise). Shouldn’t the goal simply be to maximize long-term after tax growth of your entire portfolio? If this takes the form of dividend paying stocks, so be it. But what if small caps are poised to outperform? What if you want to take Buffet’s or Bogle’s advice and just buy a broad market index like the S&P 500, (no matter what the dividend because you’ll just have it automatically reinvested to avoid the transaction fees).
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.