The CVC (Card Validation Code) or CVV (Card Validation Value) is a safety feature on credit cards. This credit card security number is to prevent the use of counterfeit or stolen credit card information, because, with the help of it, it can be determined, whether or not the credit card really exists. It can only be verified by the issuing financial institution, because there is no mathematical connection to the card number. The number combination is printed on the back of the card (not embossed) and therefore not machine readable.
You find the CVC or CVV on the back of your credit card (Mastercard, Visa). They are the last three numbers of the number combination printed level with the signature box.