The phrase "merchant gift" refers to a present or item given by a seller or shop owner to their customers as a token of appreciation or as a marketing tactic to encourage them to buy more. Full definition
An option to redeem AAdvantage miles for merchant gift cards exists and is available to Gold, Platinum or Executive Platinum elite members, or for anyone with a minimum balance of 25,000 miles. (rewardexpert.com)
You can also use points for merchant gift cards and statement credits. (rewardexpert.com)
Alternatively, you could buy merchant gift cards to pay for goods and services you are planning to purchase to get 4.5 x on a wider variety of spending. (rewardexpert.com)