A boom microphone is a general term for any type of Microphone attached to a boom pole, which is either carried or fixed to a heavy stand. Boom mics are popular in the entertainment world because they can capture audio from outside a camera frame without sacrificing quality.
Not to be confused with Studio Microphone or any desk-mounted microphones, because Boom Microphones are connected to a much longer pole and generally only seen in a film-making context.