What is the Card Security Code?

The card security code is a three-digit number (four-digit on American Express) printed on your credit card. This number is not embossed on the card and hence not printed on receipts - making it difficult for anyone other than the genuine cardholder, to know it and to use it.

Visa You will find this three-digit security code of Visa, Mastercard and Diners club credit card printed at the top of the signature strip on the reverse of the card.
American Express You will find this four-digit number security code of American Express credit card printed on the front of the card, above the account number