Boom

A boom can mean different things:

A boom is a low-pitched sound, often reverberant.  The sound of thunder and the sound of an explosion are often called booms.
A boom is a long bar:
 used in sailing and windsurfing to hold the sail.
 used in waterskiing for the beginning skier to hold onto.
 used in movies and television to hold microphones.
Boom is a municipality in Belgium