Here's a breakdown:
* Jet engines work by ingesting air, compressing it, and then burning fuel to create a hot, high-pressure gas. This gas is then expelled out of the back of the engine, creating thrust that propels the aircraft forward.
* The word "jet" comes from the stream of hot gas that is ejected from the engine, resembling a "jet" of water or another liquid. This characteristic stream of hot gas is a defining feature of jet engines.
Therefore, the "jet" in "jet airplane" refers to the jet engines that power these aircraft.