The card security code (CSC) is usually a 3 or 4 digit number, which is not part of the credit card number. The CSC is typically printed on the back of a credit card (usually in the signature field).
On some cards, all or part of the card number appears before the CSC, for example, 1234 567. In this example, 1234 are the last four digits of the credit card number, and 567 is the CSC.
Card Security Code location on non-American Express cards
On American Express cards, this code is called the Card ID and is located on the face of the card to the upper-right.
Card ID location on American Express cards
American Express is a registered trademark of the American Express Company.
