Nordic countries; Scandinavian countries
Refers to the group of countries in Northern Europe, typically including Denmark, Finland, Iceland, Norway, and Sweden. In everyday Japanese, it is often used interchangeably with 北欧 (ほくおう), but 北欧諸国 explicitly emphasizes the collection of nations.
The Nordic countries are known for their well-developed welfare systems.
I plan to travel to the Nordic countries next summer.