"Verified by Visa" is a program established by Visa to add an additional layer of security to your on-line credit card purchases.

When you register your card in the "Verified by Visa" program, you are provided with an additional password to verify that the on-line use of the card is approved by you, instead of an unauthorized user.

I have been asked for my "Verified by Visa" password in approximately a dozen on-line purchases, most of them being airline tickets.

Here is the website to register your card:
https://usa.visa.com/personal/security/vbv/index.jsp

Here are the FAQs about the program:
http://usa.visa.com/personal/securit..._visa_faq.html