What is a hangar as relating to airplanes?

A hangar is a large building where aircraft are kept, both for protection from the elements and for repairs. The same term is also applied to similar buildings that house submarines.

The term aerodrome is usually used for a hangar where old planes are kept to show them off to other people and to preserve them.

Be VERY careful to avoid confusing hangar with the soundalike word hanger, which is a hook that's used to hold an object; e.g. clothing, lamps, etc. Many people erroneously use the term "airplane hanger", but the only airplane hangers are found in museums where planes are suspended from the ceiling.