main occupation, primary business
いいか、これが俺の本業だ
Listen, this is my real job.
— ムーンライズ・キングダム (2012)
隊長の本業は何ですか？
What is the captain's main job?
本業は何だ
What's your main line of work?
— TAXi (1998)
タクシーは俺の本業じゃない
Driving a taxi isn't my main job.
本業は何か別の仕事を？
Is your main job something else?
— es［エス］ (2001)