side job; sideline; subsidiary business
彼は子供の教育費を貯めるため、週末に副業を始めた。
To save for his children's education, he started a side job on weekends.
大手企業が従業員の副業を正式に認めた。
A major corporation officially approved side jobs for its employees.
彼女は副業で本業に匹敵する収入を得ている。
She is earning income from her side job comparable to her main job.