CVV is the three or four digit number on your card that adds an extra layer of security when making purchases online or over the phone. It serves to verify that you have a physical copy of the card in your possession and helps protect you if your card number falls into the hands of hackers and identity thieves
CCN is credit card number (15 for Amex or 16 digital numbers for Visa, Mastercard , Discover..)
also CVV and CVV2 actually refer to the same thing , the security code printed on your credit card.