One who, or that which, stands by one in need; something upon which one relies for constant use or in an emergency.
- One that can always be relied on, as in an emergency.
- A favorite or frequent choice.
- One kept in readiness to serve as a substitute.
- Kept in reserve for use when needed: a standby generator.
- Of, relating to, or waiting for unreserved travel space that is made available by an airline only shortly before departure: standby passengers.
- On a standby basis: flew standby to New York.
- on standby Ready and waiting.