5 C.F.R. § 610.102
In this subpart:
Administrative workweek means any period of 7 consecutive 24-hour periods designated in advance by the head of the agency under section 6101 f title 5, United States Code.
Agency means an Executive agency and a military department as defined by sections 105 and 102 of title 5, United States Code.
Basic workweek, for full-time employees, means the 40-hour workweek established in accordance with § 610.111 .
Employee means an employee of an agency to whom this subpart applies.
Head of agency means the head of an agency or an official who has been delegated the authority to act for the head of the agency in the matter concerned.
Regularly scheduled administrative workweek, for a full-time employee, means the period within an administrative workweek, established in accordance with § 610.111 , within which the employee is regularly scheduled to work. For a part-time employee, it means the officially prescribed days and hours within an administrative workweek during which the employee is regularly scheduled to work.
Regularly scheduled work means work that is scheduled in advance of an administrative workweek under an agency's procedures for establishing workweeks in accordance with § 610.111 .
Tour of duty means the hours of a day (a daily tour of duty) and the days of an administrative workweek (a weekly tour of duty) that constitute an employee's regularly scheduled administrative workweek.
5 C.F.R. §610.102
5 U.S.C. 5548 and 6101(c)