Cash flow refers to the movement of cash into or out of a business, a project, or a financial product. It is usually measured during a specified, finite period of time. Measurement of cash flow can be used as followed:
Cash flow is a generic term used differently depending on the context. It may be defined by users for their own purposes. It can refer to actual past flows, or to projected future flows. It can refer to the total of all the flows involved or to only a subset of those flows. Subset terms include 'net cash flow', operating cash flow and free cash flow.
Common methods include:
Investors cash flow refers to the movement of cash into or out of your own pocket. An asset is something that puts money in your pocket, and a liability is something that takes money out of your pocket. 
Seen from a cash flow perspective, an asset is something that puts money in your pocket, and a liability is something that takes money out of your pocket.  The definition of cash flows for this purpose does not include increases in unrealized in share values, since such capital appreciation represents accessible cash to the shareholders only when it is paid or liquidated.
The definition of “total return,” however includes not only reported dividends, but increases in share values, since such capital appreciation represents accessible cash to the shareholders because they can liquidate their holdings at any moment in time.  But it does not provide cash flow now.
1590s, from caisse money box, 16c originally the money box, but the secondary sense of the money in it became sole meaning 18c. To convert to cash (as a check, etc.) is first attested 1811. Cash crop is attested from 1869; cash flow from 1954; cash register from 1879.  Flow from float, swim, go by sea, to flow, navigate, to pour out, rinse, flowing.