What is the difference between jet and airplane?

Answer 1

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."