California Code, Elections Code - ELEC § 6882

For purposes of this chapter, “income tax return” means any tax or information return, declaration of estimated tax, or claim for refund required by, or provided for or permitted under, the provisions of the Internal Revenue Code, and that is filed on behalf of, or with respect to any person, and any amendment or supplement thereto, including supporting schedules, attachments, or lists that are supplemental to, or part of, the return so filed.