What is a balloon?
A balloon is a latex rubber flexible bag that can be inflated with a gas or liquid.  If you want a balloon to float you can inflate it with helium.  It can also be filled with a liquid like water to make it a water balloon.  Other types of balloons are hot air balloons filled with flammable gas that go up thousands of feet in the sky and can carry people, or weather balloon which floats high into the atmosphere to measure different weather patterns.