The term 'Fly Without an Engine' can be summarized as gliding, which is a form of flight that does not require the use of an engine. Gliding is a type of unpowered flight where the aircraft uses the natural lift generated by its wings to stay in the air. This type of flight is usually done in a sailplane, which is a type of aircraft specifically designed for gliding. Gliding is a popular recreational activity and is also used in some military applications.