A 3-digit CVV, or card verification value, is a number printed on the back of all Visa, Mastercard, and Discover credit cards and debit cards as a security measure. On American Express cards, the CVV is a 4-digit number printed on the front of the card. Providing this number when making phone or online purchases helps reduce the risk of credit card fraud. The CVV may also be referred to as a card verification code (CVC) or card security code (CSC), among other names.