A promotional offer where customers who clear a spend threshold get a bonus product free. GWP is one of the engineered offers (alongside bundles and tiered thresholds) that beat a flat sitewide percent-off: it feels generous but costs you cost-of-goods, not margin-off-revenue, and the threshold pulls AOV up instead of just discounting the basket the customer already had. Pick something low-cost with high perceived value. Run it underneath any sitewide headline, never as an afterthought - and build and QA the mechanics well before peak, because a GWP that silently fails at checkout gives away margin or breaks the sale at the worst possible moment.
Benchmark. The test is margin maths: a well-chosen GWP costs COGS on the gift, while a flat percent-off gives away margin on every item in the cart. Set the threshold above current AOV so the offer grows baskets - never run a flat percent-off alone.