The Card Verification Value (CVV) is a three or four-digit number found on credit and debit cards. It is used to enhance security during online transactions, ensuring that the person making the purchase has physical possession of the card. The CVV is not stored with the card number, making it harder for fraudsters to misuse card information. When making a purchase, customers are often required to enter the CVV along with their card number and expiration date. This additional step helps protect against unauthorized transactions and is a standard practice among major card networks like Visa, MasterCard, and American Express.