A CVV code (Card Verification Value) is a three- or four-digit number found on credit and debit cards, typically located on the back of Visa, MasterCard, and Discover cards, or on the front of American Express cards. This code is used as an additional security measure to verify that the person making an online or phone transaction physically possesses the card. Merchants request the CVV code during transactions to help prevent unauthorized use of card numbers obtained through data breaches or other means. While the CVV enhances transaction security, it should never be shared or stored insecurely, as it is a target for cybercriminals in phishing attacks and card-not-present fraud.