overseas assignment; overseas posting
Refers to being sent by one's company to work in a foreign country, typically for a fixed term.
He is going to Singapore next month on an overseas assignment.
Since my overseas posting was decided, we will be moving as a family.
海外出張 is a short-term trip abroad for a specific business purpose, while 海外赴任 is a longer-term overseas job posting or transfer.
Compound of 海外 (overseas) and 赴任 (proceeding to a new post).