Investing in a local business can be a risky proposition but one with good returns if you're able to do it successfully. Becoming a silent partner is great because you don't need to do any work – it can be less great if the business doesn't do well. Sometimes you can become a silent partner in a business because they need cash and are unable to get financing from the bank – this was common during the last recession. A perfectly good business with cash flow issues is the ideal target for this type of investment.
Not everyone is eager to do this, but consider renting out space in your home for extra income. You could take in a full-time boarder, for example, but you needn't be that extreme. Instead, consider renting out an extra room via a service such as airbnb.com or homewaway.com. If you do so for just 20 nights a year and charge $100 per night, that's $2,000 in pre-tax income! If your home is in a desirable spot, maybe you can rent out the whole house for just two weeks in the summer, charging $2,000 per week and collecting $4,000.
For a person working for a wage, their source of income is their job, or their labor (aka their time that they sell to someone). But you can own a house, and rent it out, and when your renters pay you renter every month, the source of that income check is your rental property, or your house. It would just be called rental income. If you have money in the bank in an account that pays interest, those interest payments are another source of income. We can say the source is interest payments, or we can identify the asset that is generating rent, and say your money in the bank that is generating “rent” (aka interest) is your source of income.