undeclared income; unreported earnings
Refers to income or earnings that were not reported, especially in tax contexts. Often used in phrases like 申告漏れが発覚する (undeclared income comes to light).
See also: 脱税
The tax office pointed out my undeclared income.
申告漏れがないか、もう一度確認してください。
Please double-check that there is no unreported income.