Active duty. Full-time duty in the Uniformed Services of the United States. It includes duty on the active list, full-time training duty, annual training duty, and attendance while in the active Military Service, at a school designated as a Service school by law or by the Secretary of the Military Department concerned.
32 CFR § 199.2
General. In an effort to be as specific as possible as to the word and intent of CHAMPUS, the following definitions have been developed. While many of the definitions are general and some assign meaning to relatively common terms within the health insurance environment, others are applicable only to CHAMPUS; however, they all appear in this part solely for the purpose of the Program. Except when otherwise specified, the definitions in this section apply generally throughout this part.