A reserve or substitute.
reinforcements
A copy of a file or record, stored separately from the original, that can be used to recover the original if it is destroyed or damaged.
An accumulation of material caused by a (partial) obstruction or (complete) blockage of the flow or movement of the material, or an accumulation of material that causes an overflow due to the flow being greater than the maximum possible flow.
Supporting, reinforcing; (music) of or related to accompaniment
Standby, reserve or extra.
That is intended as a backup.
A state of readiness without immediate involvement; remaining in preparation for (a sudden or unforeseen event or situation).
Something that is standard, well-tested, or frequently used.
sleep mode
Waiting at the airport in the hope of getting a seat on a flight that is already booked out.
To wait briefly, as for additional communication by radio or telephone; alternative spelling of stand by