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, reducing the risk of fraud. Typically, the CVV code is located on the back of Visa, MasterCard, and Discover cards, while American Express cards have a four-digit CVV on the front. When making a purchase, entering the CVV code is often required to complete the transaction safely.