The card security code is a special code feature of your credit card to provide added security for your transaction. It is a 3- or 4-digit number which is not part of your credit card number. It appears only on your credit card and provides some
assurance the card is in your possession
Discover®, Visa® and MasterCard® have the code in the last 3 digits of the number printed on the back of the card in the signature field (see example below on the left).
American Express® has 4 digits printed on the front of the credit card on the right side above the imprinted card number (see example below on the right).