backup
⇄
adj. 1. kept in readiness or reserve.
Ex. The A.E.C. requires a pumping system to keep the reactor cool. If the primary source of power for the pumps fails, a ""backup"" system must take over to keep the coolant flowing (Wall Street Journal).
backup
⇄
backup, noun, adjective.
backup
⇄
noun 1. something or someone kept in reserve as a substitute or for assistance.
Ex. a backup of troops.
2. an accumulation.
Ex. a backup of traffic. Slow demand for steel is causing a backup along the entire raw material supply channel