The coffee shop is running twofers this week, so you get a free drink with every purchase.

twofers 是 two for one 的缩写形式，字面意思是"两个换一个"，即"买一送一"的促销活动。twofers 是商业促销用语，表示购买一件商品可以免费获得第二件相同的商品。