Complex sentence: The IC company name is an abbreviation of Integrated Coach (previously Integrated Chassis), alluding to the single corporate structure (Navistar International) that produces the bus body, chassis, and engine.
Split into simpler sentences: The IC company name stands for Integrated Coach (originally Integrated Chassis), alluding to how the vehicles are nearly completely assembled under a single corporate structure. For all IC vehicles, Navistar produces the bus body, chassis, and engine.