The hot air balloon is one example of an aerostat.
aerostat definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
an airship, balloon, or other aircraft that is lifted and sustained by means of one or more containers filled with a gas lighter than air
Origin: French aérostat: see aero- and amp; -stat
aerostat definition by American Heritage Dictionary
An aircraft, especially a balloon or dirigible, deriving its lift from the buoyancy of surrounding air rather than from aerodynamic motion.
Origin: French aérostat : Greek āero-, aero-; see aero- + Greek statos, standing; see stato-.
- aerˌo·statˈic, aerˌo·statˈi·cal adjective