For the purposes of this chapter: “Adoption assistance state” means the state that is signatory to an adoption assistance agreement in a particular case. “Residence state” means the state of which the child is a resident by virtue of the residence of the adoptive parents. “State” means a state of the United States, the District of Columbia, the Commonwealth of Puerto Rico, the Virgin Islands, Guam, the Commonwealth of the Northern Mariana Islands, or a territory or possession of or administered by the United States.