in some context, they are interchangeable while in other context, they are not."waiguo" means "foreign country/countries", whereas "guowai" means "outside your home country". "waiguo" is normally used as adjective, like waiguoren (foreigner) ore waiguohuo (foreign products). "guo wai" is a prepositional phrase, following verbs, like i live in guowai; i went guowai. e.g. i live in "waiguo", emphasizing it is a foreign country that you're living in, while i live in "guowai", emphasize the fact that you are not living in your home country, but "i live in "guowai" is used more commonly. when you refere to the people, foreigners, you can only say "waiguoren". we don't say "guowairen". in most circumstances, they are interchangeable and can be understood well.

ɡuówài =out of china wàiɡuó= other countires when you use them, most of the time, they are interchangable: 1. wǒ qù ɡuówài wán=wǒ qù wàiɡuó wán 2.ɡuówài de dōnɡxi hěn ɡuì = wài ɡuó de dōnɡxi hěn ɡuì SO PAY ATTENTION TO THE EXCEPTION we can only use "wài ɡuó rén " to refer to foreigner, instead of "ɡuó wài rén"

例子，我对你说，你是一个外国人！ 本国家，自己祖国以外的国家，都叫外国，中国人对于你来说，就是外国人！ 外国，本国相对应。 国外，就是我们的国家以外，一般用于本土人，两方都是同一个国家的人互相对话之间！ 例子，A问B，国外真的很好玩吗？ 国内，国外相对应！

"wàiguó" emphasizes a concept of nations. Such as "our country" and "their countries"; or "wàiguó ren", which means his citizenship is different from ours. "guówài" focuses on a geographic concept, which means "out of our country". When we say someone is at "guówài", it means he is abroad and he is not in our country.

相对于中国人来说，除了中国的领土就叫国外；除了中国，世界上其它的国家叫外国.