what is a security code

A security code, also known as a card security code (CSC), is a series of numbers used as a security feature for "card not present" transactions, such as online or over-the-phone purchases. It is a three- or four-digit number that is not part of the credit card number and is typically printed on the back of a credit or debit card, in the signature field. The security code is designed to prevent fraudulent transactions and is used to provide protection against fraud in online and over-the-phone transactions