Section 31.7701-2 - Definitions; spouse, husband and wife, husband, wife, marriage(a)In general. For the definition of the terms spouse, husband and wife, husband, wife, and marriage, see § 301.7701-18 of this chapter.(b)Applicability date. The rules of this section apply to taxable years ending on or after September 2, 2016.T.D. 9785, 81 FR 60616 , Sept. 2, 2016 T.D. 9785, 81 FR 60616, 9/2/2016