In this chapter,

(1) “bank” means a financial institution including a national banking association;

(2) “corporation” includes an association, joint-stock company, and an insurance company;

(3) “fiscal year” means an accounting period of 12 months ending on the last day of a month other than December;

(4) “includes” and “including” when used in a definition do not exclude other things otherwise within the meaning of the word defined;

(5) “Internal Revenue Code” means the Internal Revenue Code of the United States (26 U.S.C.) as the code exists now or as hereafter amended, as the code and amendments apply to the normal taxes and surtax on net incomes, which amendments are operative for the purposes of this chapter as of the time they became operative or will become operative under federal law;

(6) “part-year resident” means an individual who enters or leaves the state during the taxable year and who has resided or was domiciled in the state for a period of less than 12 months during the taxable year;

(7) “person” means an individual, a trust or estate, or partnership, or a corporation;

(8) “taxable year” means the calendar year or the fiscal year ending during the calendar year upon the basis of which the net income is computed under this chapter; “taxable year” includes, in the case of a return made for a fractional part of a year under this chapter, the period for which the return is made;

(9) “taxpayer” means a person subject to a tax imposed by this chapter;

(10) “trade or business” includes the engaging in or carrying on of a trade, business, profession, vocation, employment, and rendition of services or commercial activity and includes the performance of the function of a public office.