An instant rebate, or sometimes instant savings, is a marketing strategy or gimmick in which a product is either advertised at a specific price, or at a discounted price, where the discount is applied at the time of purchase. For example, the store may advertise a widget for $9.99, but with a $5 instant rebate, the price is $4.99. Or the product may be advertised as $4.99 with a $5 instant rebate.
Instant rebates are different from a "standard" rebate. Under normal circumstances, a rebate is given to a customer who mails in a coupon along with proof of purchase, and is mailed a check by the manufacturer or the rebate processor. In the case of an instant rebate, the rebate is provided immediately, at the instant of purchase.
We can see instant rebate as a discount on a product. In accounting strategy the actual invoice will be less by the amount of the instant rebate that is given to the customer. Then:
invoice cost = the product cost - instant rebate amount.