You use overseas to describe things that involve or are in foreign countries, usually across a sea or an ocean.
foreign
He has returned to South Africa from his long overseas trip.
他结束了漫长的海外旅行回到了南非。
overseas trade figures.
外贸数据。
An overseas student or visitor comes from a foreign country, usually across a sea or an ocean.
Every year nine million overseas visitors come to the city.
每年有900万的海外游客来到这座城市。
firmly targeted at overseas buyers.
锁定海外买家。
If you go overseas, you go to a foreign country, usually across a sea or an ocean
If you're staying for more than three months or working overseas, a full 10-year passport is required.
如果在海外居留或工作3个月以上,须持有效期为10年的护照。