Income (cash flow): This is often called positive cash flow after all expenses are paid, including my mortgage payment and taxes.
Depreciation (phantom cash flow): This appears as an expense when it's really income that comes from a tax break. This confuses many people who are new to investing in real estate; it's essentially income you don't see.
Amortization: This is income because your tenant is paying down your loan. Paying the mortgage on your personal residence is an expense, but when your tenant pays your loan down, it's cash flow.
Appreciation: This is really inflation that appears as appreciation. If your rental income goes up, you as an investor can refinance and borrow your appreciation out as tax-free cash, and have your tenant pay for the amortization of the new loan amount. In other words, it can be tax-free cash flow.