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