What is a Card Security Code (CSC/CVV2)?

The security code is a three or four digit code printed (not imprinted or stamped) on your card. On Mastercard ,Visa, and Discover, the code is usually on the back of the card, to the right of the last four digits of the card number.

On American Express, it is usually on the front of the card, above the card number.

American Express Example