Security code also known as "CVV" is an important security feature for credit card transactions on the Internet and over the phone. "CVV" stands for "Card Verification Value
Visa, Mastercard, Discover
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 security code 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 security code enhances fraud protection and helps to validate credit card possession.