on standby

Từ điển Oxford Advanced Learner 8th

on ˈstandby idiom
1. ready to do sth immediately if needed or asked
•The emergency services were put on standby after a bomb warning.
•As the level of the water rose, villages were put on evacuation standby.
•The troops are on 24-hour standby (= ready to move at an time of the day or night).
2. ready to travel or go somewhere if a ticket or sth that is needed suddenly becomes available
•He was put on standby for the flight to New York.
Main entry: ↑standby_idiom