American Express Membership Rewards points are the points you earn on Amex consumer rewards cards (those that aren’t co-branded to earn another points currency, like Hilton Honors Bonus Points or Delta SkyMiles).
You earn Membership Rewards points by using your card for purchases within qualifying categories that earn points. If you have multiple points-earning rewards cards with Amex, they will automatically pool into your Membership Rewards account each billing cycle. Then you can choose how you’d like to redeem.