The noun 军队 (jūnduì) means "army," "troops," or "armed forces." It is a general term for organized military personnel. You will encounter it frequently in news reports and discussions about national defense or conflict.
这个国家的军队总共有五十万人。
Zhège guójiā de jūnduì zǒnggòng yǒu wǔshí wàn rén.
This country's military has a total of five hundred thousand personnel.
军队已经被派往灾区参与救援工作。
Jūnduì yǐjīng bèi pàiwǎng zāiqū cānyù jiùyuán gōngzuò.
The military has already been dispatched to the disaster area to participate in rescue operations.
他十八岁就加入了军队。
Tā shíbā suì jiù jiārùle jūnduì.
He joined the military at the age of eighteen.