stand‧by1 , stand-by plural standbys
ready to help immediately if you are needed:
A special team of police were kept on standby.
b)➔ stand by (4)
if you are on standby to do something, for example to travel by plane, you are on a list of people who may be allowed to do it if places become available, for example if other people cannot use their tickets:
We can put you on standby.
something that is kept ready so that it can be used when needed:
Powdered milk is a good standby in an emergency.