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A bank check having insufficient funds to back it.
A check that a bank refuses to honor because there is not enough money in the payer's checking account to cover the amount of the check. For example, if Bob writes Joe a check for $200, but there is only $175 in Bob's account, then Bob has written a not-sufficient-funds check and the bank will refuse to transfer the funds to Joe's account. It is also called an NSF check, a bad check or a returned check.