Refers to a flight that requires a transfer at an intermediate airport to reach the final destination.
I plan to transfer to a connecting flight at Narita.
乗り継ぎ is the general act of transferring between any vehicles, not limited to flights.
直行便 goes straight to the destination with no stops, while 乗り継ぎ便 requires changing planes at least once.
Standard full kanji spelling.
Abbreviated kanji spelling, common in signs and schedules.
Compound of 乗り継ぎ (transfer, connecting) + 便 (flight, service).