Many people in the investment world also define residual income as revenue stemming from a passive source. This revenue is created without a direct input of effort or time. The investment itself creates addition revenues without having to be managed. Some examples include royalties, dividends, interest, and rent. Take a dividend stock for example. Once the money is invested once, it will keep producing a dividend every year without having to input additional time or resources. This concept is the Holy Grail for most investors.

Build an investment portfolio that pays out dividends (Stocks / Bonds / Mutual Funds). Dividends are payouts that companies give to their investors as a portion of their earnings. They’re often paid out quarterly. If you’ve already got an investment portfolio, it’s time to take a good look at which stocks, bonds, or mutual funds you own. You’ll see consistent returns from the ones that pay dividends. This is a fantastic way to earn passive income. Invest once and watch the returns pile up.

For example, you can design digital products, like animal clipart or a downloadable wedding poem that could be printed by the customer. Your design could be resold thousands of times without needing to create each item or ship it. Once you create your digital product and list it on a site like Etsy or Ebay, the revenue flows in with little oversight.
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.