[countable] (plural standbys) a thing or person that can always be used if needed, for example if sth/sb else is not available or if there is an emergency
後备人员；备用品◆I have a laptop as a standby in case my computer crashes.
万一我的计算机崩溃了，我另外还有一台膝上型电脑备用。 ●on ˈstandby

1. ready to do sth immediately if needed or asked
   待命◆We are on standby to increase production if demand increases.
   如果需求增长我们随时准备增加产量。