越南 (Yuènán) is a proper noun meaning "Vietnam." It is the standard Chinese name for the country, composed of 越 (Viet) and 南 (south). It is used in geographical, cultural, and political contexts.
他去越南出差了,下周才回来。
tā qù Yuènán chūchāi le, xià zhōu cái huílái.
He went to Vietnam on a business trip and won't be back until next week.
越南的咖啡在世界上很有名。
Yuènán de kāfēi zài shìjiè shàng hěn yǒumíng.
Vietnamese coffee is very famous in the world.
我计划暑假去越南旅游。
wǒ jìhuà shǔjià qù Yuènán lǚyóu.
I plan to travel to Vietnam during summer vacation.