When a bank suffers a sudden rush of withdrawals by depositors, this is called a bank run. Since banks lend out most of the cash they receive in deposits (see fractional-reserve banking), it is difficult for them to quickly pay back all deposits if these are suddenly demanded, so a run may leave the bank in bankruptcy, causing many depositors to lose their savings unless they are covered by deposit insurance. A situation in which bank runs are widespread is called a systemic banking crisis or just a banking panic. A situation without widespread bank runs, but in which banks are reluctant to lend, because they worry that they have insufficient funds available, is often called a credit crunch.
When a country that maintains a fixed exchange rate is suddenly forced to devalue its currency because of a speculative attack, this is called a currency crisis or balance of payments crisis. When a country fails to pay back its sovereign debt, this is called a sovereign default. While devaluation and default could both be voluntary decisions of the government, they are often perceived to be the involuntary results of a change in investor sentiment that leads to a sudden stop in capital inflows or a sudden increase in capital flight.