Cash flow essentially refers to the study of cycle of cash inflows and outflows of a business, a project, or a financial product. In accounting terms, cash flow refers to the difference between the available cash at the beginning of an accounting period and that at the end of the period. If the closing balance is higher than the opening balance, then cash flow is positive. Conversely, it is negative if the opening balance is higher than the closing balance. Sales, loan proceeds, investments and the sale of assets etc. result in cash inflow while operating and direct expenses, principal debt service, and the purchase of assets etc. result in cash outflow. Cash flow indicates the health of a company or a project a positive cash flow a business/project may not survive, even if it is profitable. It is used for a number of purposes like determination of a project's rate of return or value. Cash flow is also used to determine problems with a business's liquidity and to find the quality of earnings.