Internal Revenue Code section 61
Section 61 of the Internal Revenue Code (IRC 61, 26 U.S.C. § 61) defines "gross income", the starting point for determining which items of income are taxable for federal income tax purposes in the United States. Section 61 states that "[e]xcept as otherwise provided in this subtitle, gross income means all income from whatever source derived [ . . .
Source: Wikipedia — Internal Revenue Code section 61 (CC BY-SA 4.0)