When you spend more money than you have in your bank account, or the amount of money you owe the bank for doing this.
Compound of 'over' (beyond/more than) and 'draft' (withdrawal of money). Emerged as banking terminology in the 19th century as modern checking accounts developed.
Banks make billions in overdraft fees by allowing people to spend money they don't have and then charging them for it—this is a deliberately designed trap that disproportionately affects poor people who live paycheck to paycheck.
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