Meaning:
“睡” means “sleep,” “后” means “after,” and “收入” means “income.” A homophone of “税后收入,” which means “after-tax income,” this term refers to “passive income,” or “money you can earn without needing to be physically present — even in your sleep.” In the United States, there are basically three types of taxable income: earned income (also called active income), portfolio income (derived from investments) and passive income (real estate and certain business arrangements, such as limited partnerships). In Chinese, this term seems to cover both passive and portfolio income, although managing a portfolio is in fact a taxing job.
Example:
A: 小林就是个普通公务员，但日子过得很滋润，为什么？
Xiǎolín jiù shì gè pǔtōng gōngwùyuán，dàn rìzi guò de hěn zīrùn，wèishénme？
Xiaolin is a junior civil servant but he lives high on the hog. How could he?
B: 因为他有睡后收入啊。他前些年买了好几套房，光收租都比每个月的工资多几倍。
Yīnwèi tā yǒu shuìhòu shōurù a。Tā qiánxiēnián mǎi le hǎo jǐtào fáng，guāng shōuzū dōu bǐ měige yuè de gōngzī duō jǐbèi。
Because he has passive income. He bought several apartments years ago, and the rents are several times his monthly salary.