国旗 (guóqí) means "national flag" and refers to the official flag of a country. It appears in phrases like 和国旗一样的颜色 (the same colors as the national flag) and 升国旗 (raise the national flag).
每个星期一学校都会举行升国旗仪式。
měi gè xīngqīyī xuéxiào dōu huì jǔxíng shēng guóqí yíshì.
Every Monday the school holds a flag-raising ceremony.
天安门广场上的国旗每天都按时升降。
Tiān'ānmén guǎngchǎng shàng de guóqí měitiān dōu ànshí shēngjiàng.
The national flag at Tiananmen Square is raised and lowered on schedule every day.
他看到自己国家的国旗,心里很激动。
tā kàn dào zìjǐ guójiā de guóqí, xīnlǐ hěn jīdòng.
When he saw his country's national flag, he felt very moved.