Operating working capital is the difference between current assets and current liabilities used in the day to day trading operations of a business. In most businesses this amounts to inventory plus accounts receivable less accounts payable, which represents the funding needed to buy inventory and provide credit to customers, reduced by the amount of credit obtained from suppliers.
Any net change in inventory, accounts receivable or accounts payable over an accounting period, results in a corresponding net change in business working capital. As the other side of the entry has to be represented by cash, the change in working capital represents a cash flow which is included as part of the cash flow statement.