When many bank customers try to withdrawal their bank deposits simultaneously, and the bank's reserves are not sufficient to cover the withdrawals Bank run's are synonymous with panic
A series of unexpected cash withdrawals caused by a sudden decline in depositor confidence or fear that the bank will be closed by the chartering agency, i e many depositors withdraw cash almost simultaneously Since the cash reserve a bank keeps on hand is only a small fraction of its deposits, a large number of withdrawals in a short period of time can deplete available cash and force the bank to close and possibly go out of business [FRBM][FRBSF] (see also bank)
Before deposit insurance, when the depositors in a bank fear that it is insolvent, and so all at once in a group demand that the bank liquidate their deposits for cash