A gas balloon is a type of aircraft that remains aloft by means of buoyancy created by a gas contained within an envelope. The most typical gas used is helium.
These aircraft are sometimes called Charlière after Jacques Charles who designed the first aircraft of this type. Charles and Ainé Robert made the first person-carrying flight of such an aircraft on December 1, 1783.
Gas balloons differ from hot air balloons in that no fuel is burned to heat the lifting gas.
Gas balloons are distinct from airships in that airships can be steered and propelled upwind whereas gas balloons drift with the wind.
Gas balloons differ from moored balloons in that moored balloons remain in one place whereas gas balloons are free flying and move with the wind.