Otherwise referred to as an "NSF" or "Returned Item".  Non Sufficient funds is when your bank account does not have suffiicient funds to cover a check or other debit transaction.  This can occur frequently in faxless payday loan transactions when your loan payment is due, and the payday lender tries to debit your account for the amount due.  NSF fees can be VERY expensive (the national average charged by banks is over $25)!  Make sure that you know exactly when a debit is going to hit your bank account, and make sure you have enough money in the account to cover the debit.  Payday loans are expensive enough — don't add to the expense by bouncing a payment and incurring an additional NSF fee (or two).  If you won't have enough funds in your account when the loan is due, make sure to CALL YOUR LENDER before the due date to see if you can work something out.