a piece of paper that can be used to pay for particular goods or services or that allows you to pay less than the usual price for them

The voucher is valid between July and December and entitles you to ten percent off all overseas flights. 该代金券在7月至12月间有效，凭此券所有国际航班可享受9折的优惠。

in the US, a scholarship (= money to pay for studies) that allows a student to attend a private school rather than a state school

Suburban voters are completely against vouchers. 郊区选民完全反对私立学校奖学金。