An airliner is a type of aircraft initially designed for the transportation of paying passengers.
There may be variants developed for air freight, military or luxury corporate use. Occasionally the military version precedes the civilian airliner. Examples are the Boeing KC-135 and Boeing 707/720 series and, looking to the future, perhaps the Bell-Boeing MV-22 Osprey. Corporate or military use may follow the withdrawal of the airplane from use as a passenger transport, possibly for reasons of economy or environmental restraint. Most airliners are owned or leased by airlines.