Most credit cards now include a 3 or 4 digit verification number, which is not part of the regular credit card number. CVD seeks to ensure that the purchaser has the physical card in hand when placing a phone, mail, or Internet order, and to verify that the card account is legitimate. The number is not contained in the magnetic strip information nor does it appear on sales receipt.
For most cards, the CVD number is a three digit number on the back of the card.
American Express cards have a four digit CVD number on the front, above the credit card number.