In expensive cities like San Francisco and New York City, net rental yields can fall as low as 2%. This is a sign that there is a lot of liquidity buying property for property appreciation, and not so much for income generation. This is a riskier proposition than buying property based on rental income. In inexpensive cities, such as those in the Midwest, net rental yields can easily be in the range of 8% – 12%, although appreciation may be slower.

Writing and publishing an eBook has become a widely popular means of earning passive income in recent years. eBooks on non-fiction topics like online marketing, business development, career advice, and the like are especially successful. While fiction eBooks are also good sellers, the market for them is much more competitive as compared to non-fiction ones. Once you've written an eBook, you can put it up for sale on platforms like Amazon's Kindle Direct Publishing or Apple's iTunes Connect.
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.