pk and voucher

pk is a chiglish word.
come up from a game term"player kill".
the term pk is popularized by one famous show"super girls".
meaning of pk, I think, almost equals "competition".
so, today's pk is a kind of competition, about how to dress, make ourselves fashion.

shopping voucher:does it fit to be used to describe something which customers can use as money for shopping?
oh, who can tell me?
gift certificate?gift coupon?