The Card Security Code (CSC) or Card Verification Value(CVV) is a 3- or 4-digit number used to help verify that a debit or credit card payment is being submitted by the card holder.
For Visa, MasterCard, and Discover debit or credit cards, the CSC is the 3-digit number located on the back of the card, usually printed to the right of the signature strip. On some cards, all or part of the credit card number will appear before the CSC.