"出差"用英语表达为 "on a business trip".
"Business"在英语中有"商业"的意思，而 "trip"则表示"旅行"。因此 "on a business trip"意为"出差"。
例句：
I'll be on a business trip next week. (下周我要出差)
She's always on business trips, so she hardly ever sees her family. (她总是出差，所以很少见到家人)
My boss is on a business trip in Tokyo. (我的老板正在东京出差)