CVV2 (Card Verification Value, Second Generation) is a three-digit value that is uniquely derived for each credit card account. It is printed in reverse italic characters on the signature panel of all Visa and MasterCard cards following the last 4 digits of the account number.
In a card-not-present environment such as the Internet, CVV2 lets a merchant verify that the cardholder does in fact have the card in his or her possession.