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 balloon in that the moored balloons remain in one place whereas free flying move with the wind.