Duty free usually refers to shops or retail outlets that are exempt from paying local or national taxes. This is all based on the goods being sold to people who are traveling and will take the items out of the country. It is common to find these stores in most airports around the world.

It refers to retail stores that are free from certain local or national taxes and duties.

Those are the shops at the airports for example where you can pay tax free. So, sometimes little cheaper.