What is the difference between jet and airplane?
Any fixed-wing aircraft with an engine is an airplane. There are
different kinds: piston-engine airplanes have piston engines
driving propellers, (airplane engines are horizontally-opposed,
like the engine in an old Volkswagen), turboprop airplanes have
turbine engines with gearboxes that drive propellers, and jet
airplanes have turbine engines that move the plane directly.
So, factually, a jet is a type of engine on an airplane.
However, over time, aircraft with jet engines have often been
referred to as "jets."