Hey Chinmay Jain,
Thanks for using Apple Support Communities.
For more information, take a look at:
iTunes Store: My credit card's security code or zip code does not match my bank's records
http://support.apple.com/kb/ts1646
When there is a mismatch between the iTunes Store's records and your credit card company's records, you will receive an error message stating that your credit card's security code isn't valid
Have a nice day,
Mario