national flag
Refers to the official flag of a country. A straightforward, common noun.
オリンピックの開会式で各国の国旗が掲げられた。
The national flags of each country were raised at the Olympic opening ceremony.
The national flag is hoisted in the schoolyard.
The climber planted the national flag at the summit.
The spectators waved national flags to cheer on the athletes.
The national flag fluttered in the strong wind.