What typically indicates a flight is on 'stand-by'?

A flight is typically considered to be on 'stand-by' when it is fully booked. In this scenario, passengers who do not have confirmed seats are placed on a waitlist in hopes of getting onto the flight in case any booked passengers do not show up or cancel at the last minute. Stand-by travelers are often hopeful that there will be available seats due to these unforeseen circumstances.

While a flight being overbooked might also suggest stand-by situations, it is primarily the full booking status that defines it clearly. In overbooked flights, passengers may have bought tickets, but the term 'stand-by' is more directly associated with those without guaranteed seats trying to board a flight that is already at capacity.