CVV2 is an important security feature for credit card transactions on the Internet and over the phone. “CVV” stands for “Card Verification Value” (Discover Card calls it the “Cardmember ID”). It is the three-digit number printed in the signature space on the back of most credit cards, such as Visa, Mastercard, and Discover cards. The CVV2 number is always the last group of numbers in the signature space on the back of the card. It is not part of your regular credit card number. It is a four-digit number on the front of American Express cards. It is printed (flat), not embossed like the card number.
The number enhances fraud protection and helps to validate two things: the customer has the credit card in their possession and the credit card number is legitimate.