A credit card security code is a unique three of four digit number, seperate from your credit card number, used to authenticate account details and protect against fraud.
Flip your card over and look at the signature box. You should see either the entire 16-digit credit card number or just the last four digits followed by a special 3-digit code. This 3-digit code is your Card Security Code.
Look for the 4-digit code printed on the front of your card just above and to the right of your main credit card number. This 4-digit code is your Card Security Code.