from The American Heritage® Dictionary of the English Language, 4th Edition
- n. One that can always be relied on, as in an emergency.
- n. A favorite or frequent choice.
- n. One kept in readiness to serve as a substitute.
- adj. Kept in reserve for use when needed: a standby generator.
- adj. Of, relating to, or waiting for unreserved travel space that is made available by an airline only shortly before departure: standby passengers.
- adv. On a standby basis: flew standby to New York.
- idiom on standby Ready and waiting.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. State of readiness without being immediately involved.
- n. Waiting at the airport in the hope of getting a seat on a flight that is already booked out.
- n. Something that is standard, well-tested, or frequently used.
- v. Wait briefly: alternative spelling of stand by.
From stand + by. (Wiktionary)