A cash flow is a real or virtual movement of money:

• a cash flow in its narrow sense is a payment (in a currency), especially from one central bank account to another; the term 'cash flow' is mostly used to describe payments that are expected to happen in the future, are thus uncertain and therefore need to be forecast with cash flows;
• a cash flow is determined by its time t, nominal amount N, currency CCY and account A; symbolically CF = CF(t,N,CCY,A).
• it is however popular to use cash flow in a less specified sense describing (symbolic) payments into or out of a business, project, or financial product.

Cash flows are narrowly interconnected with the concepts of value, interest rate and liquidity. A cash flow that shall happen on a future day t_N can be transformed into a cash flow of the same value in t₀. This transformation process is known as discounting, and it takes into account the time value of money by adjusting the nominal amount of the cash flow based on the prevailing interest rates at the time.