N-VAR
备用品；后备计划
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...
系统的每个部分都有备用元件。
Computer users should make regular back-up copies of their work.
计算机使用者应该定期对自己的工作进行备份。