An airliner is a type of transport aircraft for transporting passengers and air cargo. Such aircraft are most often operated by airlines. The largest airliners are called "wide-body aircraft". These aircraft are frequently called "twin-aisle aircraft" because they generally have two separate aisles running from the front to the back of the passenger cabin. These aircraft are usually used for long-haul flights between airline hubs and major cities with many passengers. A smaller, more common class of airliners is the "narrow-body aircraft" or "single aisle" aircraft. These smaller airliners are generally used for short to medium-distance flights with fewer passengers than their wide-body counterparts.