coupon [coupons](section of a ticket giving the holder some entitlement) noun [UK: ˈkuː.pɒn] [US: ˈkuː.ˌpɒn]
voucher [vouchers](a piece of paper that entitles the holder to a discount, or that can be exchanged for goods and services) noun [UK: ˈvaʊ.tʃə(r)] [US: ˈvaʊ.tʃər]