A Boom

1. (nautical) A spar extending the foot of a sail; a spar rigged outboard from a ship's side to which boats are secured in harbour.
2. A movable pole used to support a microphone or camera.
3. (by extension) A microphone supported on such a pole.
4. A horizontal member of a crane or derrick, used for lifting.
5. (electronics) The longest element of a Yagi antenna, on which the other, smaller ones are transversally mounted.
6. A floating barrier used to obstruct navigation, for military or other purposes; or used for the containment of an oil spill or to control the flow of logs from logging operations.
7. A wishbone-shaped piece of windsurfing equipment.
8. The section of the arm on a backhoe closest to the tractor.
9. A gymnastics apparatus similar to a balance beam.