When withdrawing money to live on, I don’t care how many stock shares I own or what the dividends are – I care about how much MONEY I’m able to safely withdraw from my total portfolio without running out before I die. A lot of academics have analyzed total market returns based on indices and done Monte Carlo simulations of portfolios with various asset allocations, and have come up with percentages that you can have reasonable statistical confidence of being safe.
The U.S. Internal Revenue Service categorizes income into three broad types, active income, passive income, and portfolio income. It defines passive income as only coming from two sources: rental activity or "trade or business activities in which you do not materially participate." Other financial and government institutions also recognize it as an income obtained as a result of capital growth or in relation to negative gearing. Passive income is usually taxable.
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.