Affiliate marketing is the practice of partnering with a company (becoming their affiliate) to receive a commission on a product. This method of generating income works the best for those with blogs and websites. Even then, it takes a long time to build up before it becomes passive. If you want to get started with affiliate marketing check out this great list of affiliate marketing programs.
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.