According to 8 USCS § 1151 [TITLE 8. Aliens and Nationality; Chapter 12. Immigration and Nationality Immigration Selection System], the term "immediate relatives" means "(A) the children, spouses, and parents of a citizen of the United States, except that, in the case of parents, such citizens shall be at least 21 years of age. In the case of an alien who was the spouse of a citizen of the United States and was not legally separated from the citizen at the time of the citizen's death, the alien (and each child of the alien) shall be considered, for purposes of this subsection, to remain an immediate relative after the date of the citizen's death but only if the spouse files a petition under section 204(a)(1)(A)(ii) [8 USCS § 1154(a)(1)(A)(ii)] within 2 years after such date and only until the date the spouse remarries. For purposes of this clause, an alien who has filed a petition under clause (iii) or (iv) of section 204(a)(1)(A) of this Act [8 USCS § 1154(a)(1)(A)] remains an immediate relative in the event that the United States citizen spouse or parent loses United States citizenship on account of the abuse.
(ii) Aliens admitted under section 211(a) [8 USCS § 1181(a)] on the basis of a prior issuance of a visa to their accompanying parent who is such an immediate relative.
(B) Aliens born to an alien lawfully admitted for permanent residence during a temporary visit abroad.