What does the term "No Show" refer to?

The term "No Show" specifically refers to a situation where a customer has made a reservation for a flight but does not arrive to check in or board the aircraft. This can have implications for the airline's operations, including affecting the availability of seats for other passengers, as well as potential financial impacts due to lost revenue.

In contrast, the other options represent different scenarios that do not align with the definition of a "No Show." A passenger missing a connecting flight indicates that they were present for the initial leg of their journey but were unable to continue; a crewmember reporting for duty pertains to flight staff being present and ready to work; and a passenger successfully boarding a flight shows that they are present and checked in. All these scenarios highlight passenger or crew presence or actions relevant to travel, but do not encapsulate the definition of "No Show."