The card security code is a unique three or four digit, non embossed security number, associated to your credit card number, as illustrated below.
Visa / MasterCard
The three-digit card verification code (CVV or CVC2) is non embossed and typically printed on the signature panel of your card, immediately after the card's standard number, as show in this example. In some cases you may see the last 4 digits of your card number with the additional 3 digit security code following.
The card security code for your American Express card is a four-digit card identification number (CID or 4DBC) located on the front of your credit card, above your main credit card number, as illustrated.