For Visa, MasterCard, and Discover cards, the card code is the last 3 digit number located on the back of your card on or above your signature line. For an American Express card, it is the 4 digits on the FRONT above the end of your card number.
To help reduce fraud in the card-not-present environment, credit card companies have introduced a card code program. Visa calls this code Card Verification Value (CVV); MasterCard calls it Card Validation Code (CVC); Discover calls it Card ID (CID). The card code is a three- or four- digit security code that is printed on the back of cards. The number typically appears at the end of the signature panel.