The Constitution of the United States of America makes reference to income, but does not define it. No law in the USC defines income.
"Income" in federal courts is treated to suggest any acquisition of Federal Reserve currency, or acquisition of any thing that can be converted to Federal Reserve currency.
Lil Wayne: Ya man, that boy spits out A Milli-Milli-Milli times better than me.
Drake: Yeh, hes hardworking too. I guess he wants to be Successful.
Lil Wayne: Hes piling up the income.