reserve equipment; backup unit; spare
Refers to equipment kept in reserve for use when the primary equipment fails or is unavailable. Common in technical, industrial, and military contexts.
We keep backup equipment ready in case of a power outage.
In this factory, reserve equipment is always stored in case the main machinery breaks down.
Compound of 予備 (yobi, 'reserve, spare') and 装置 (sōchi, 'equipment, device').