The CVC/CVV code is a card verification number. Each credit card has one.
The purpose of this verification number is to combat the fraudulent use of forged or stolen credit card details in online transactions.
The CVC/CVV code is a three-digit number combination that is printed (not embossed) on the back of every credit card. It can only be verified by the credit card issuer, because it is not mathematically related to the card number in any way.
In connection with online transactions, but also for reservations (hotel, car hire, etc.) that you make either online or by phone, the service provider may require you to provide this code in order to process payment via your credit card.