Definition of Gross Income 26 USC §61-Gross Income Defined Cornell University: Gross Income Defined http://www.law.cornell.edu/uscode/text/26/61 IRS code section 61 section 61(a) http://www.law.cornell.edu/uscode/text/26/61 26 USC § 61 IRS code section 61 26 U.S.C. § 61. Gross income defined gross income