The CVV identification code is located on the back of the credit card, the last three digits of the 7-digit number on the signature line (the first four digits are the last four digits of the card number), the specific location is shown in the picture:

It is Like the validity period, it is used for security verification during special transactions such as online payment/telephone authorization, so it must be kept well and cannot be leaked. Moreover, there is a security code for each card, and the bank cannot check it. You can only keep it yourself.