16 CFR §1513.2

As used in this part 1513: Bed. See Bunk bed. Bed end structure means an upright unit at the head and foot of the bed to which the side rails attach. Bunk bed means a bed in which the underside of any foundation is over 30 inches (760 mm) from the floor. Foundation means the base or support on which a mattress rests. Guardrail means a rail or guard on a side of the upper bunk to prevent a sleeping occupant from falling or rolling out.