5 C.F.R. § 359.802

For the purpose of this subpart, furlough means the placing of an appointee in a temporary status without duties and pay because of lack of work or funds or other nondisciplinary reasons; except it does not refer to an emergency shutdown furlough caused by a lapse in congressional appropriations where the ultimate duration of the furlough is not known by the agency at the outset of the furlough.