What is the CVV?
CVV stands for Credit Card Validation (or Verification) Value. Visa has a version of the CVV to reduce merchant risk in Card-Not-Present transactions (like Internet, telephone or mail-order). The CVV code adds assurance that the consumer placing the order has access or physical possession of the credit card itself. The CVV is a 3 digit number embossed or imprinted on the reverse side of Visa cards.

Where do I find the CVV?
For Visa the 3 digit CVV number is printed on the signature panel on the back of the card immediately after the card's account number.