What is an iTunes card generator?
An iTunes Card is Apple's version of a Gift Card. It comes in a different range of values ($10, $15, $25, $50 or $100) and it can be used to redeem any item of the iTunes Store, App Store, iBooks Store, and Mac App Store.

An iTunes Card Generator is a software which allegedly generates these gift codes, so that you can acquire anything from the aforementioned stores without actually paying anything.