• (n.) One who, or that which, stands by one in need; something upon which one relies for constant use or in an emergency.
Stand'-by` noun One who, or that which, stands by one in need; something upon which one relies for constant use or in an emergency. 
wait, stop and wait.
[v] - not act or do anything 2. [v] - be loyal to 3. [v] - be available or ready for a certain function or service
stick verb be loyal to; `She stood by her husband in times of trouble`; `The friends stuck together through the war`
This is a service where you wait at the airport until the next seat becomes available on your chosen route. Stand-by tickets used to be a cheap way to travel, sad to say those days are over. Nowadays stand-by applies more to employees of airlines who can use up available seats very cheaply.