But, you don't need to go further than that. You can simply write it and publish it and collect the income. That's all. Send out a couple emails to your list (if you have one) or post it on social media, and there you have it. Passive income. Now, the amount of income you receive depends on the quality of the book you've written. How well did you craft the message? How targeted was the information to your audience? It counts.

3. Start as soon as possible. Building a livable passive-income stream takes a tremendously long time, largely because of declining interest rates since the late 1980s. Gone are the days of making a 5%-plus return on a short-term CD or savings account. Today, the best 12-month CD is at 2.5%, and the best money-market rate is about 1.85%, which is not bad, considering such rates were below 0.5% just a couple of years ago. Know that every $100 you save can generate at least $2.5 in passive income.

Residual income is the amount of net income generated in excess of the minimum rate of return. Residual income concepts have been used in a number of contexts, including as a measurement of internal corporate performance whereby a company's management team evaluates the return generated relative to the company's minimum required return. Alternatively, in personal finance, residual income is the level of income that an individual has after the deduction of all personal debts and expenses have been paid.