coupon

/ˈkuˌpɔn/

a negotiable certificate that can be detached and redeemed as needed

中文释义：优惠券；票券

She used a coupon to get 20% off her grocery bill.

她用了一张优惠券，在杂货账单上省了20%。

The store offers digital coupons that can be scanned from your phone.

这家商店提供可以从手机扫描的数字优惠券。