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side job (outside of one's main employment); side gig; side hustle
homeworking; simple job carried out at home; home industry
(secretly) working on something unrelated to the class (or conference, etc.) one is attending
妻は家計を助けるために内職している。
My wife does piecework from home to help with household expenses.
学生は内職で学費を賄う。
Students cover their tuition fees with a side job.
彼女は内職で貯めたお金で、新しいカメラを購入した。
She bought a new camera with the money she saved from her side job.