CVV2
Credit Card Verification Value Coded is a security feature for credit or debit card transactions transactions occurring over the Internet, by mail, fax or over the phone. The CVV2 is designed to give an increased protection against credit card fraud. The CVV2 number is required to be entered in at transaction time to verify the card is on hand.
This number is printed on your Visa, MasterCard, & Discover cards in the signature area of the back of the card. (it is the last 3 digits AFTER the credit card number in the signature area of the card
American Express cards show the CVV2 printed above and to the right of the imprinted card number on the front of the card.