5 U.S.C. § 5561

For the purpose of this subchapter— (1) “agency” means an Executive agency and a military department; (2) “employee” means an employee in or under an agency who is a citizen or national of the United States or an alien admitted to the United States for permanent residence, but does not include a part-time or intermittent employee or native labor casually hired on an hourly or daily basis. However, such an employee who enters a status listed in paragraph (5)(A)–(E) of this section— (A) inside the continental United States; or (B) who is a resident at or in the vicinity of his place of employment in a territory or possession of the United States or in a foreign country and who was not living there solely as a result of his employment; is an employee for the purpose of this subchapter only on a determination by the head of the agency concerned that this status is the proximate result of employment by the agency; (3) “dependent” means— (A) a wife; (B) an unmarried child (including an unmarried dependent stepchild or adopted child) under 21 years of age; (C) a dependent mother or father; (D) a dependent designated in official rec­ords; and (E) an individual determined to be dependent by the head of the agency concerned or his designee; (4) “active service” means active Federal service by an employee; (5) “missing status” means the status of an employee who is in active service and is officially carried or determined to be absent in a status of— (A) missing; (B) missing in action; (C) interned in a foreign country; (D) captured, beleaguered, or besieged by a hostile force; or (E) detained in a foreign country against his will; but does not include the status of an employee for a period during which he is officially determined to be absent from his post of duty without authority; and (6) “pay and allowances” means— (A) basic pay; (B) special pay; (C) incentive pay; (D) basic allowance for housing; (E) basic allowance for subsistence; and (F) station per diem allowances for not more than 90 days.