Passengers or airline staff flying without a confirmed reservation are placed on a waitlist to fill empty seats just before departure. Gate agents clear this list in order of priority, usually based on frequent flyer status or employee seniority, once all confirmed passengers have boarded. If the flight departs full, the remaining waitlisted travelers are rolled over to the next departure.
Heard on the job
We've three no-shows in coach, so go ahead and clear the first three non-revs on standby.