noun
additional income; extra income; side income
Refers to income earned in addition to one's main salary, such as from a side job, investments, or rental property.
彼は副収入を得るために週末にアルバイトをしている。
He works a part-time job on weekends to earn extra income.
副収入があれば、
If you have additional income, you can have more financial leeway.