principal occupation; core business; main job
Refers to one's primary profession or the main line of business, as opposed to a side job or secondary activity.
His main job is a teacher, but he works part-time at a café on weekends.
当社の本業はソフトウェア開発です。
Our company's core business is software development.
He makes music his main profession.
Besides his main job, he paints as a hobby.
I decided to quit my side job and focus fully on my main occupation.
It's not easy to balance one's main job with raising children.