N-VAR
備用品；后備計劃
If you have something such as a second piece of equipment or set of plans as backup, you have arranged for them to be available for use in case the first one does not work.
例句
Every part of the system has a backup...
系統的每個部分都有備用元件。
Computer users should make regular back-up copies of their work.
計算機使用者應該定期對自己的工作進行備份。