1) DEBT not dept
2) IF you have an overdraft (spend more than is in the account) protection, then it is possible to wind up owing the bank the overages.
A "Debit Card" is also referred to as a "Check Card" because, like a check, the money is drawn DIRECTLY from your account.
Those that think the MC/Visa logo means it's also a Credit Card don't know their @ss from their elbow. The MC/Visa aspect allows the merchant to run the debit card like a credit card (signature, not a PIN) but the money is still debited directly from your account.
Merchants PREFER to run it as a debit card because it's a Flat Rate of 80 - 90 cents per transaction, regardless of the amount of the sale. As a Credit Card, the "discount" (the fee the merchant pays for the convenience of accepting cards) is a Percentage of 2.5 - 3% of the transaction. So, a $1000 sale would cost the merchant $30 if run as a credit card. But as a debit card, the transaction costs him only 85 cents if it's $10 or $10,000. BUT, the merchant may not have the equipment to run it as a debit card.