The definition of grey income. Before the reform and opening up, there was no such term as "grey income" in mainland China; after the reform and opening up, the economy became increasingly active, and the income of various social groups became diversified. People refer to legitimate wages, bonuses, subsidies, etc. as "white income", and illegal income as "black income". As for a kind of income that lies between white and black, people cannot clearly explain it, and more often than not, it is inconvenient to point out. "You know and I know that's enough", thus the term "grey income" came into being.