GRE/Some questions about Credit Card

1. Can anyone please tell me what is a "security code " of a credit card ?

Diagram of a credit card.

Flip your card to the back side, the side that contains the magnetic strip. You will see a bunch of numbers therein. The last three numbers are usually your security code.

In case your service regards a different set of numbers as the security code, they will say so on the website. Watch out clearly for instructions. Usually, there will be a small hyperlink underlined by blue next to the question on security code that says "What's this?" Click on it to find out what exactly the particular website assumes to be the security code.

If in confusion, contact the webmaster, or us, or someone else who knows and uses credit cards regularly.