The CVV Number ("Card Verification Value") on your credit card or debit card is a 3 digit number on VISA®, MasterCard® and Discover® branded credit and debit cards. On your American Express® branded credit or debit card it is a 4 digit numeric code.
CVV numbers are also known as CVC numbers ("Card Verification Code"), CSC numbers ("Card Security Code"), or CVV2 numbers, which are the same as CVV numbers, except that they have been generated by a 2nd generation process that makes them harder to "guess".