Duty-free goods are goods bought in special shops in airports, on ships, etc. on which you do not pay government tax.

He bought his wife some duty-free perfume. 他给妻子买了一些免税香水。

I bought some perfume in the duty-free shop. 我在免税店买了一些香水。

goods that you can buy in special shops in airports, on ships, etc., without paying tax on them

We can buy our duty-free while we're waiting at the airport. 我们在机场候机时可以买些免税商品。

a shop at an airport, on a ship, etc. where you can buy duty-free goods

There'll be a duty-free on the ferry. 轮船上有免税商店。