A CVV code, or Card Verification Value, is a three or four-digit number found on credit and debit cards. It is used to enhance security during online and card-not-present transactions. The CVV code helps verify that the person making the purchase has physical possession of the card. Typically, the CVV code is located on the back of a credit card for most card issuers, while American Express cards have it on the front. Entering the CVV code during a transaction helps protect against fraud and unauthorized use of the card.