The Card Security Code (CSC), sometimes called Card Verification Value or Code (CVV or CVC), is a security feature for credit or debit card transactions, giving increased protection against credit card fraud.
There are actually two security codes:
1.The first code, called CVC1 or CVV1,is encoded on the magnetic strip of the card and used for transactions in person.
2. The second code, and the most cited, is CVV2 or CVC2. This CSC (also known as a CCID or Credit Card ID) is often asked for by merchants for them to secure "card not present" transactions occurring over the Internet, by mail, fax or over the phone. In many countries in Western Europe, due to increased attempts at card fraud, it is now mandatory to provide this code when the cardholder is not present in person.
This latter CSC should not be confused with the standard card account number appearing in embossed or printed digits. (The standard card number undergoes a separate validation algorithm called the Luhn algorithm which serves to determine whether a given card's number is appropriate.)