a person or thing that can always be used if needed, for example if somebody/something else is not available or if there is an emergency
ذخیره, پشتیبان, فرد جایگزین, نیروی جایگزین
adjective
1
a standby ticket for a flight, concert, etc. cannot be bought in advance and is only available a very short time before the plane leaves or the performance starts